[SPARK-13583][CORE][STREAMING] Remove unused imports and add checkstyle rule

## What changes were proposed in this pull request?

After SPARK-6990, `dev/lint-java` keeps Java code healthy and helps PR review by saving much time.
This issue aims remove unused imports from Java/Scala code and add `UnusedImports` checkstyle rule to help developers.

## How was this patch tested?
```
./dev/lint-java
./build/sbt compile
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11438 from dongjoon-hyun/SPARK-13583.

3 files changed, 4 insertions, 4 deletions

diff --git a/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLCLIDriver.scala b/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLCLIDriver.scala
index fb31119a9e..79cf7e8378 100644
--- a/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLCLIDriver.scala
+++ b/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLCLIDriver.scala
@@ -32,14 +32,15 @@ import org.apache.hadoop.hive.common.{HiveInterruptCallback, HiveInterruptUtils}
 import org.apache.hadoop.hive.conf.HiveConf
 import org.apache.hadoop.hive.ql.Driver
 import org.apache.hadoop.hive.ql.exec.Utilities
-import org.apache.hadoop.hive.ql.processors.{AddResourceProcessor, CommandProcessor, CommandProcessorFactory, SetProcessor}
+import org.apache.hadoop.hive.ql.processors.{AddResourceProcessor, CommandProcessor,
+  CommandProcessorFactory, SetProcessor}
 import org.apache.hadoop.hive.ql.session.SessionState
 import org.apache.thrift.transport.TSocket
 
 import org.apache.spark.Logging
 import org.apache.spark.sql.AnalysisException
 import org.apache.spark.sql.hive.HiveContext
-import org.apache.spark.util.{ShutdownHookManager, Utils}
+import org.apache.spark.util.ShutdownHookManager
 
 /**
  * This code doesn't support remote connections in Hive 1.2+, as the underlying CliDriver
diff --git a/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLDriver.scala b/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLDriver.scala
index 4278aa30fb..0eb2627e7a 100644
--- a/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLDriver.scala
+++ b/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLDriver.scala
@@ -25,7 +25,6 @@ import org.apache.commons.lang3.exception.ExceptionUtils
 import org.apache.hadoop.hive.metastore.api.{FieldSchema, Schema}
 import org.apache.hadoop.hive.ql.Driver
 import org.apache.hadoop.hive.ql.processors.CommandProcessorResponse
-import org.apache.log4j.LogManager
 
 import org.apache.spark.Logging
 import org.apache.spark.sql.AnalysisException
diff --git a/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/ui/ThriftServerTab.scala b/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/ui/ThriftServerTab.scala
index 1dc7d79436..63e6bbcfee 100644
--- a/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/ui/ThriftServerTab.scala
+++ b/sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/ui/ThriftServerTab.scala
@@ -18,7 +18,7 @@
 package org.apache.spark.sql.hive.thriftserver.ui
 
 import org.apache.spark.{Logging, SparkContext, SparkException}
-import org.apache.spark.sql.hive.thriftserver.{HiveThriftServer2, SparkSQLEnv}
+import org.apache.spark.sql.hive.thriftserver.HiveThriftServer2
 import org.apache.spark.sql.hive.thriftserver.ui.ThriftServerTab._
 import org.apache.spark.ui.{SparkUI, SparkUITab}