Backed out changeset f117d9332a08 (bug 1607205) for causing gtest crashes.

media/webrtc/signaling/src/media-conduit/AudioConduit.cpp

@@ -1014,8 +1014,6 @@ void WebrtcAudioConduit::DeleteRecvStream() {
     mCall->Call()->DestroyAudioReceiveStream(mRecvStream);
     mRecvStream = nullptr;
   }
-  mRecvChannelProxy->SetRtcpEventObserver(nullptr);
-
   // Destroying the stream unregisters the transport
   mRecvChannelProxy->RegisterTransport(nullptr);
 }