Remove unused val

Author: andrewor14

core/src/main/scala/org/apache/spark/deploy/master/Master.scala

@@ -72,9 +72,7 @@ private[spark] class Master(
   val waitingApps = new ArrayBuffer[ApplicationInfo]
   val completedApps = new ArrayBuffer[ApplicationInfo]
   var nextAppNumber = 0
-
   val appIdToUI = new HashMap[String, SparkUI]
-  val fileSystemsUsed = new HashSet[FileSystem]
 
   val drivers = new HashSet[DriverInfo]
   val completedDrivers = new ArrayBuffer[DriverInfo]
@@ -159,7 +157,6 @@ private[spark] class Master(
       recoveryCompletionTask.cancel()
     }
     webUi.stop()
-    fileSystemsUsed.foreach(_.close())
     masterMetricsSystem.stop()
     applicationMetricsSystem.stop()
     persistenceEngine.close()