Fix Win VideoSendStream::...::ToString() compiles.

Removed an extra ::VideoSendStream in the method declarations.

BUG=3171
TBR=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/21469004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6171 4adac7df-926f-26a2-2b94-8c16560cd09d