Remove duplicate RegisterReceiver message

  - The ReceiverTracker receivers `RegisterReceiver` messages two times
     1) When the actor at `ReceiverSupervisorImpl`'s preStart is invoked
     2) After the receiver is started at the executor `onReceiverStart()` at `ReceiverSupervisorImpl`

Though, RegisterReceiver message uses the same streamId and the receiverInfo gets updated everytime
the message is processed at the `ReceiverTracker`, it makes sense to call register receiver only after the
receiver is started.

streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceiverSupervisorImpl.scala

@@ -77,13 +77,6 @@ private[streaming] class ReceiverSupervisorImpl(
   /** Akka actor for receiving messages from the ReceiverTracker in the driver */
   private val actor = env.actorSystem.actorOf(
     Props(new Actor {
-      override def preStart() {
-        logInfo("Registered receiver " + streamId)
-        val msg = RegisterReceiver(
-          streamId, receiver.getClass.getSimpleName, Utils.localHostName(), self)
-        val future = trackerActor.ask(msg)(askTimeout)
-        Await.result(future, askTimeout)
-      }
 
       override def receive() = {
         case StopReceiver =>