Move CallStats to Call, EncoderStateFeedback to VideoSendStream and remove last ViEChannel dependency from ChannelGroup. BUG=webrtc:5079 R=pbos@webrtc.org, stefan@webrtc.org Review URL: https://codereview.webrtc.org/1418613002 . Cr-Commit-Position: refs/heads/master@{#10355}