Removing old channel code from a few more places.

Plus adding peer connection close event.

R=jiayl@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/37509004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7982 4adac7df-926f-26a2-2b94-8c16560cd09d