Allow picking TURN/UDP or TURN/TCP in url params

Also, clean up some legacy TURN-related URL parameters that were
obsolete.  You can now specify a HTTP URL for TURN via ts=, but the
previous ts, tp, ss parameters are now defunct.

PTAL @jiayl, @tkchin
That's actually part of the turn URI syntax, e.g. turn:foo.example.com?transport=tcp. I can remove it if you think it is confusing, or expand the comment.