Remove ViESender.

Registers transport on construction removing the need for ViESender as a
hop and removing a potential deadlock by removing RegisterSendTransport.

BUG=1695, 2999
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/57449004

Cr-Commit-Position: refs/heads/master@{#9309}
13 files changed