Delete method VCMJitterBuffer::RegisterStatsCallback

Unused in the legacy VideoCodingModule api since
https://webrtc-review.googlesource.com/c/src/+/62101/
and unused by the VideoReceiveStream code path since
https://webrtc-review.googlesource.com/c/src/+/128870

Bug: webrtc:7408
Change-Id: I800dba08a6e0e8f5de6169241d217bd5e8e5d0de
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/129961
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27319}
diff --git a/modules/video_coding/include/video_coding_defines.h b/modules/video_coding/include/video_coding_defines.h
index 81ec68d..0998610 100644
--- a/modules/video_coding/include/video_coding_defines.h
+++ b/modules/video_coding/include/video_coding_defines.h
@@ -84,7 +84,9 @@
   virtual void OnCompleteFrame(bool is_keyframe,
                                size_t size_bytes,
                                VideoContentType content_type) = 0;
+  // TODO(nisse): Delete.
   virtual void OnDiscardedPacketsUpdated(int discarded_packets) = 0;
+  // TODO(nisse): Delete.
   virtual void OnFrameCountsUpdated(const FrameCounts& frame_counts) = 0;
   virtual void OnFrameBufferTimingsUpdated(int decode_ms,
                                            int max_decode_ms,