[webrtc-pc] Pull Request: Removed legacy getStats() method.

alvestrand has just submitted a new pull request for 
https://github.com/w3c/webrtc-pc:

== Removed legacy getStats() method. ==
Discussion in #924 showed that nobody intends to implement as
specified, so keeping it for "legacy" is not helpful.

Closes #924

See https://github.com/w3c/webrtc-pc/pull/985