Delete some dead code in vcm::VideoReceiver and VCMReceiver

Bug: None
Change-Id: I9cb8bd57af697762a9fc76007e139695afaf1fa4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/152381
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29134}

modules/video_coding/receiver.h

@@ -42,7 +42,6 @@ class VCMReceiver {
 
   ~VCMReceiver();
 
-  void Reset();
   int32_t InsertPacket(const VCMPacket& packet);
   VCMEncodedFrame* FrameForDecoding(uint16_t max_wait_time_ms,
                                     bool prefer_late_decoding);
@@ -54,10 +53,7 @@ class VCMReceiver {
                        int max_incomplete_time_ms);
   std::vector<uint16_t> NackList(bool* request_key_frame);
 
-  void TriggerDecoderShutdown();
-
  private:
-  rtc::CriticalSection crit_sect_;
   Clock* const clock_;
   VCMJitterBuffer jitter_buffer_;
   VCMTiming* timing_;