Remove simulcast modules from ViEReceiver.

Instead of maintaining two lists of simulcast modules, deliver RTCP
packets to simulcast modules inside ViEChannel.

BUG=1695
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/48119004

Cr-Commit-Position: refs/heads/master@{#9027}
3 files changed