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_coding_impl.h

@@ -132,7 +132,6 @@ class VideoReceiver : public Module {
   // These callbacks are set on the construction thread before being attached
   // to the module thread or decoding started, so a lock is not required.
   VCMFrameTypeCallback* _frameTypeCallback;
-  VCMReceiveStatisticsCallback* _receiveStatsCallback;
   VCMPacketRequestCallback* _packetRequestCallback;
 
   // Used on both the module and decoder thread.