Added url params arbr, asbr, vrbr & vsbr to apprtc.

Added url params arbr, asbr, vrbr & vsbr to apprtc demo to control audio
and video send/receive bitrate.
BUG=3166
Revert "Added url params arbr, asbr, vrbr & vsbr to apprtc."

Reason for revert: CL was committed to the main repo instead of a forked repo accidentally.

This reverts commit 14bf1877407661b31902f14cb5fd8ad472939982.