[SPARK-4803] 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.