Minor - Fix trivial compilation warnings.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #2331 from ScrapCodes/compilation-warn and squashes the following commits:

44c1e76 [Prashant Sharma] Minor - Fix trivial compilation warnings.

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -49,7 +49,6 @@ import org.apache.spark.scheduler.cluster.{CoarseGrainedSchedulerBackend, SparkD
 import org.apache.spark.scheduler.cluster.mesos.{CoarseMesosSchedulerBackend, MesosSchedulerBackend}
 import org.apache.spark.scheduler.local.LocalBackend
 import org.apache.spark.storage._
-import org.apache.spark.SPARK_VERSION
 import org.apache.spark.ui.SparkUI
 import org.apache.spark.util.{CallSite, ClosureCleaner, MetadataCleaner, MetadataCleanerType, TimeStampedWeakValueHashMap, Utils}
 

examples/src/main/scala/org/apache/spark/examples/graphx/LiveJournalPageRank.scala

@@ -20,7 +20,7 @@ package org.apache.spark.examples.graphx
 import org.apache.spark.SparkContext._
 import org.apache.spark._
 import org.apache.spark.graphx._
-import org.apache.spark.examples.graphx.Analytics
+
 
 /**
  * Uses GraphX to run PageRank on a LiveJournal social network graph. Download the dataset from