Remove WebRtcVideoEngine.

Leaves a stub file for talk/media/webrtc/webrtcvideoengine.cc until
build files in Chromium have been modified.

BUG=1695,4566
R=mflodman@webrtc.org, pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/48339004

Cr-Commit-Position: refs/heads/master@{#9148}
15 files changed