Use lower level mute methods

Currently we use `setMicrophoneEnabled` and `setCameraEnabled` to mute/unmute.

Those methods are very "smart", they:
- check for existing tracks
- start tracks if required
- publish tracks if not yet published

We do all of this in dedicated sections. So letting livekit take care of this is not necessary. It actually is bad since it might race with our own track initialisation.