[webrtc-pc] new commits pushed by aboba

The following commits were just pushed by aboba to https://github.com/w3c/webrtc-pc:

* Fix prose indicating reasons why sender may be missing in removeTrack().
  by Jan-Ivar Bruaroey
https://github.com/w3c/webrtc-pc/commit/d14e657501f4ad2528c2af342151cdff6c324f03

* Merge pull request #2162 from jan-ivar/nosender

Fix prose indicating reasons why sender may be missing in removeTrack (Editorial)
  by Bernard Aboba
https://github.com/w3c/webrtc-pc/commit/5a8369fbb3273bd88f924d727c888d26b47aa324