unpublish method
Implementation
Future<void> unpublish() async {
if (_pc != null) {
var tracks = _stream.getTracks();
await _pc!
.getSenders()
.then((senders) => senders.forEach((RTCRtpSender s) async {
if (tracks.contains((e) => s.track?.id == e.id)) {
await _pc?.removeTrack(s);
}
}));
}
}