Remove extra semicolon in import statement and unused import in ApplicationMaster

Small nit cleanup to remove extra semicolon and unused import in Yarn's stable ApplicationMaster (it bothers me every time I saw it)

Author: Henry Saputra <hsaputra@apache.org>

Closes #358 from hsaputra/nitcleanup_removesemicolon_import_applicationmaster and squashes the following commits:

bffb685 [Henry Saputra] Remove extra semicolon in import statement and unused import in ApplicationMaster.scala

Author: hsaputra

yarn/stable/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala

@@ -18,7 +18,6 @@
 package org.apache.spark.deploy.yarn
 
 import java.io.IOException
-import java.net.Socket
 import java.util.concurrent.CopyOnWriteArrayList
 import java.util.concurrent.atomic.{AtomicInteger, AtomicReference}
 
@@ -36,7 +35,7 @@ import org.apache.hadoop.yarn.client.api.AMRMClient.ContainerRequest
 import org.apache.hadoop.yarn.conf.YarnConfiguration
 import org.apache.hadoop.yarn.ipc.YarnRPC
 import org.apache.hadoop.yarn.util.{ConverterUtils, Records}
-import org.apache.hadoop.yarn.webapp.util.WebAppUtils;
+import org.apache.hadoop.yarn.webapp.util.WebAppUtils
 
 import org.apache.spark.{Logging, SecurityManager, SparkConf, SparkContext}
 import org.apache.spark.deploy.SparkHadoopUtil