Revert of Fix the video buffer size should take rtt into consideration (patchset #3 id:40001 of https://codereview.chromium.org/2980413002/ )

Reason for revert:
We are not certain this is the behavior we want.

Original issue's description:
> Fix the video buffer size should take rtt into consideration
>
> BUG=webrtc:8010
>
> Review-Url: https://codereview.webrtc.org/2980413002
> Cr-Commit-Position: refs/heads/master@{#19285}
> Committed: f1e08d0b58

TBR=sprang@webrtc.org,gustavogb@gmail.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:8010

Review-Url: https://codereview.webrtc.org/3002033002
Cr-Commit-Position: refs/heads/master@{#19442}

webrtc/modules/video_coding/frame_buffer2.h

@@ -74,9 +74,6 @@ class FrameBuffer {
   // return immediately.
   void Stop();
 
-  // Updates the RTT for jitter buffer estimation.
-  void UpdateRtt(int64_t rtt_ms);
-
  private:
   struct FrameKey {
     FrameKey() : picture_id(0), spatial_layer(0) {}