[MINOR] Fix Java style errors and remove unused imports

## What changes were proposed in this pull request?

Fix Java style errors and remove unused imports, which are randomly found

## How was this patch tested?

Tested on my local machine.

Author: Xin Ren <iamshrek@126.com>

Closes #14161 from keypointt/SPARK-16437.

common/unsafe/src/main/java/org/apache/spark/unsafe/memory/HeapMemoryAllocator.java

@@ -24,7 +24,6 @@ import java.util.LinkedList;
 import java.util.Map;
 
 import org.apache.spark.unsafe.Platform;
-import org.apache.spark.unsafe.memory.MemoryAllocator;
 
 /**
  * A simple {@link MemoryAllocator} that can allocate up to 16GB using a JVM long primitive array.

common/unsafe/src/main/java/org/apache/spark/unsafe/memory/MemoryAllocator.java

@@ -23,12 +23,12 @@ public interface MemoryAllocator {
    * Whether to fill newly allocated and deallocated memory with 0xa5 and 0x5a bytes respectively.
    * This helps catch misuse of uninitialized or freed memory, but imposes some overhead.
    */
-  public static final boolean MEMORY_DEBUG_FILL_ENABLED = Boolean.parseBoolean(
+  boolean MEMORY_DEBUG_FILL_ENABLED = Boolean.parseBoolean(
     System.getProperty("spark.memory.debugFill", "false"));
 
   // Same as jemalloc's debug fill values.
-  public static final byte MEMORY_DEBUG_FILL_CLEAN_VALUE = (byte)0xa5;
-  public static final byte MEMORY_DEBUG_FILL_FREED_VALUE = (byte)0x5a;
+  byte MEMORY_DEBUG_FILL_CLEAN_VALUE = (byte)0xa5;
+  byte MEMORY_DEBUG_FILL_FREED_VALUE = (byte)0x5a;
 
   /**
    * Allocates a contiguous block of memory. Note that the allocated memory is not guaranteed

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala

@@ -780,8 +780,7 @@ private[sql] object ParquetFileFormat extends Logging {
     val assumeBinaryIsString = sparkSession.sessionState.conf.isParquetBinaryAsString
     val assumeInt96IsTimestamp = sparkSession.sessionState.conf.isParquetINT96AsTimestamp
     val writeLegacyParquetFormat = sparkSession.sessionState.conf.writeLegacyParquetFormat
-    val serializedConf =
-      new SerializableConfiguration(sparkSession.sessionState.newHadoopConf())
+    val serializedConf = new SerializableConfiguration(sparkSession.sessionState.newHadoopConf())
 
     // !! HACK ALERT !!
     //

sql/core/src/test/scala/org/apache/spark/sql/sources/DataSourceTest.scala

@@ -18,7 +18,6 @@
 package org.apache.spark.sql.sources
 
 import org.apache.spark.sql._
-import org.apache.spark.sql.internal.SQLConf
 
 private[sql] abstract class DataSourceTest extends QueryTest {