[SPARK-16535][BUILD] In pom.xml, remove groupId which is redundant definition...

[SPARK-16535][BUILD] In pom.xml, remove groupId which is redundant definition and inherited from the parent

https://issues.apache.org/jira/browse/SPARK-16535

## What changes were proposed in this pull request?

When I scan through the pom.xml of sub projects, I found this warning as below and attached screenshot
```
Definition of groupId is redundant, because it's inherited from the parent
```
![screen shot 2016-07-13 at 3 13 11 pm](https://cloud.githubusercontent.com/assets/3925641/16823121/744f893e-4916-11e6-8a52-042f83b9db4e.png)

I've tried to remove some of the lines with groupId definition, and the build on my local machine is still ok.
```
<groupId>org.apache.spark</groupId>
```
As I just find now `<maven.version>3.3.9</maven.version>` is being used in Spark 2.x, and Maven-3 supports versionless parent elements: Maven 3 will remove the need to specify the parent version in sub modules. THIS is great (in Maven 3.1).

ref: http://stackoverflow.com/questions/3157240/maven-3-worth-it/3166762#3166762

## How was this patch tested?

I've tested by re-building the project, and build succeeded.

Author: Xin Ren <iamshrek@126.com>

Closes #14189 from keypointt/SPARK-16535.

assembly/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-assembly_2.11</artifactId>
   <name>Spark Project Assembly</name>
   <url>http://spark.apache.org/</url>

common/network-common/pom.xml

@@ -26,7 +26,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-network-common_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Networking</name>

common/network-shuffle/pom.xml

@@ -26,7 +26,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-network-shuffle_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Shuffle Streaming Service</name>

common/network-yarn/pom.xml

@@ -26,7 +26,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-network-yarn_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project YARN Shuffle Service</name>

common/sketch/pom.xml

@@ -26,7 +26,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-sketch_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Sketch</name>

common/tags/pom.xml

@@ -26,7 +26,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-tags_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Tags</name>

common/unsafe/pom.xml

@@ -26,7 +26,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-unsafe_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Unsafe</name>

core/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-core_2.11</artifactId>
   <properties>
     <sbt.project.name>core</sbt.project.name>

examples/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-examples_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Examples</name>

external/flume-assembly/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-flume-assembly_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project External Flume Assembly</name>

external/flume-sink/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-flume-sink_2.11</artifactId>
   <properties>
     <sbt.project.name>streaming-flume-sink</sbt.project.name>

external/flume/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-flume_2.11</artifactId>
   <properties>
     <sbt.project.name>streaming-flume</sbt.project.name>

external/java8-tests/pom.xml

@@ -24,7 +24,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>java8-tests_2.11</artifactId>
   <packaging>pom</packaging>
   <name>Spark Project Java 8 Tests</name>

external/kafka-0-10-assembly/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-kafka-0-10-assembly_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Integration for Kafka 0.10 Assembly</name>

external/kafka-0-10/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-kafka-0-10_2.11</artifactId>
   <properties>
     <sbt.project.name>streaming-kafka-0-10</sbt.project.name>

external/kafka-0-8-assembly/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-kafka-0-8-assembly_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project External Kafka Assembly</name>

external/kafka-0-8/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-kafka-0-8_2.11</artifactId>
   <properties>
     <sbt.project.name>streaming-kafka-0-8</sbt.project.name>

external/kinesis-asl-assembly/pom.xml

@@ -25,7 +25,6 @@
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-kinesis-asl-assembly_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Kinesis Assembly</name>

external/kinesis-asl/pom.xml

@@ -25,7 +25,6 @@
   </parent>
 
   <!-- Kinesis integration is not included by default due to ASL-licensed code. -->
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-streaming-kinesis-asl_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Kinesis Integration</name>

external/spark-ganglia-lgpl/pom.xml

@@ -25,7 +25,6 @@
   </parent>
 
   <!-- Ganglia integration is not included by default due to LGPL-licensed code -->
-  <groupId>org.apache.spark</groupId>
   <artifactId>spark-ganglia-lgpl_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Ganglia Integration</name>