Remove VideoEngine interfaces.

Removes ViE interfaces, _impl.cc files, managers (such as
ViEChannelManager and ViEInputManager) as well as ViESharedData.

Interfaces necessary to implement observers have been moved to a
corresponding header (such as vie_channel.h).

BUG=1695, 4491
R=mflodman@webrtc.org, solenberg@webrtc.org
TBR=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/55379004

Cr-Commit-Position: refs/heads/master@{#9179}
168 files changed