[SPARK-4802] [streaming] Remove receiverInfo once receiver is de-regi…

…stered

  Once the streaming receiver is de-registered at executor, the `ReceiverTrackerActor` needs to
remove the corresponding reveiverInfo from the `receiverInfo` map at `ReceiverTracker`.

Author: Ilayaperumal Gopinathan <igopinathan@pivotal.io>

Closes apache#3647 from ilayaperumalg/receiverInfo-RTracker and squashes the following commits:

6eb97d5 [Ilayaperumal Gopinathan] Polishing based on the review
3640c86 [Ilayaperumal Gopinathan] Remove receiverInfo once receiver is de-registered

streaming/src/main/scala/org/apache/spark/streaming/scheduler/ReceiverTracker.scala

@@ -150,8 +150,8 @@ class ReceiverTracker(ssc: StreamingContext, skipReceiverLaunch: Boolean = false
         logWarning("No prior receiver info")
         ReceiverInfo(streamId, "", null, false, "", lastErrorMessage = message, lastError = error)
     }
-    receiverInfo(streamId) = newReceiverInfo
-    listenerBus.post(StreamingListenerReceiverStopped(receiverInfo(streamId)))
+    receiverInfo -= streamId
+    listenerBus.post(StreamingListenerReceiverStopped(newReceiverInfo))
     val messageWithError = if (error != null && !error.isEmpty) {
       s"$message - $error"
     } else {