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

  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 #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