Remove unused code, we always use replaceTrack in unified plan

MediaStreamTrack.getSettings is not implemented.

* feat(video-quality): control the sender resolution based on video quality settings

* fix(video-quality): Apply the settings on newly created p2p/jvb jingle sessions
If a p2p/jvb session is not present when setSenderVideoConstraint is called,
make sure the settings are applied when they are created

Make sure we don't have a=simulcast lines on the sendonly m-lines in the remote description

Trigger renegotiation only for plan-b when tracks are muted or unmuted

Enabled desktop sharing and discontinue support for Safari versions prior to 12.1, i.e., the ones with no VP8 support

Switch to using ontrack for remote tracks, re-use mids/transceivers when remote sources are removed and added.

Co-Authored-By: Saúl Ibarra Corretgé <s@saghul.net>

Trigger renegotation only when negotiationneeded event is fired on the browser.
Do not disable simulcast for screensharing in unified plan.
Fix the order of the simulcast streams for Firefox