Delete VCMJitterBuffer::UpdateRtt and related unused code

Bug: webrtc:7408
Change-Id: Ic4bd745ed36dd7f7d5eec6531e05204035a545fd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/133188
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27648}

modules/video_coding/receiver.h

@@ -43,7 +43,6 @@ class VCMReceiver {
   ~VCMReceiver();
 
   void Reset();
-  void UpdateRtt(int64_t rtt);
   int32_t InsertPacket(const VCMPacket& packet);
   VCMEncodedFrame* FrameForDecoding(uint16_t max_wait_time_ms,
                                     bool prefer_late_decoding);