Revert "Implement transceiver.stop()"

This reverts commit 11dc6571cb4ff3e71dee1557dfff8d9076e108d3.

Reason for revert: Breaks Chromium WPT tests

Original change's description:
> Implement transceiver.stop()
> 
> This adds RtpTransceiver.StopStandard(), which behaves according to
> the specification at
> https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiver-stop
> 
> It modifies RTCPeerConnection.getTransceivers() to return only
> transceivers that have not been stopped.
> 
> Rebase of armax' https://webrtc-review.googlesource.com/c/src/+/172762
> 
> Bug: chromium:980879
> Change-Id: I7d383ee874ccc0a006fdcf280496b5d4235425ce
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/180580
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#31893}

TBR=sakal@webrtc.org,kthelgason@webrtc.org,hta@webrtc.org,guidou@webrtc.org,marinaciocea@webrtc.org

Change-Id: Ibdc24f7d41e481293ca74ba6d1572de64f7e4654
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:980879
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181262
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31897}

sdk/objc/api/peerconnection/RTCRtpTransceiver.h

@@ -117,7 +117,7 @@ RTC_OBJC_EXPORT
  *  this transceiver will no longer send, the receiver will no longer receive.
  *  https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiver-stop
  */
-- (void)stopInternal;
+- (void)stop;
 
 @end