Remove unused callbacks from VideoStreamDecoder

VCMReceiveStatisticsCallback originates in the old jitter buffer, and
is no longer used.

VCMFrameTypeCallback originates in VideoReceiver::RequestKeyFrame,
which is called from OncomingPacket, Process, Decode(uint16_t
maxWaitTimeMs), all of which are unused by VideoReceiveStream.

So delete the code to wire them up via VideoStreamDecoder.

Bug: webrtc:7408
Change-Id: I173bc94eb32f2641f943c125083db038c3bcaeb1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128870
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27277}

modules/video_coding/video_receiver.cc

@@ -54,7 +54,6 @@ VideoReceiver::VideoReceiver(Clock* clock,
                 keyframe_request_sender),
       _decodedFrameCallback(_timing, clock_),
       _frameTypeCallback(nullptr),
-      _receiveStatsCallback(nullptr),
       _packetRequestCallback(nullptr),
       _scheduleKeyRequest(false),
       drop_frames_until_keyframe_(false),
@@ -197,9 +196,8 @@ int32_t VideoReceiver::RegisterReceiveStatisticsCallback(
   // |_receiver| is used on both the decoder and module threads.
   // However, since we make sure that we never do anything on the module thread
   // when the decoder thread is not running, we don't need a lock for the
-  // |_receiver| or |_receiveStatsCallback| here.
+  // |_receiver| here.
   _receiver.RegisterStatsCallback(receiveStats);
-  _receiveStatsCallback = receiveStats;
   return VCM_OK;
 }