MINOR: Removing dead code.

Meant to do this when patching up the last merge.

core/src/main/scala/org/apache/spark/scheduler/ShuffleMapTask.scala

@@ -57,7 +57,6 @@ private[spark] object ShuffleMapTask {
   }
 
   def deserializeInfo(stageId: Int, bytes: Array[Byte]): (RDD[_], ShuffleDependency[_,_]) = {
-    val loader = Thread.currentThread.getContextClassLoader
     val in = new GZIPInputStream(new ByteArrayInputStream(bytes))
     val ser = SparkEnv.get.closureSerializer.newInstance()
     val objIn = ser.deserializeStream(in)