Delete remnants of ContentHint handling in WebRtcVideoCapturerAdapter

The |content_hint_| member is unused since
https://chromium-review.googlesource.com/c/chromium/src/+/1146564/.

Deletes wiring in MediaStreamVideoWebRtcSink, as a preparation for
replacing WebRtcVideoCapturerAdapter (a subclass of
cricket::VideoCapturer) with an implementation of
webrtc::VideoTrackSourceInterface.

Bug: 864529, webrtc:6353
Change-Id: I48972c63a6c69ceb859fb11fcad98d6faefac524
Reviewed-on: https://chromium-review.googlesource.com/c/1375720
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Niels Möller <nisse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616620}
4 files changed