Remove old WebRTC-NewVideoJitterBuffer used for testing the NackModule.

This experiment was used to test the NackModule but will soon (tm) be used to
test the completly new video jitter buffer.

BUG=webrtc:5514
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2123913002 .

Cr-Commit-Position: refs/heads/master@{#13395}

webrtc/modules/video_coding/receiver.h

@@ -91,9 +91,6 @@ class VCMReceiver {
 
   void TriggerDecoderShutdown();
 
-  int64_t TimeUntilNextProcess();
-  void Process();
-
  private:
   CriticalSectionWrapper* crit_sect_;
   Clock* const clock_;