Calling removeTrack twice shouldn't throws an InvalidAccessError

[syerrapragada]

see: https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/removeTrack

If the track is already stopped, or is not in the connection's senders list, this method has no effect.

But the shim implementation throws InvalidAccessError if removeTrack is called twice.

[fippo]

This is partly due to not implementing the transceiver model. See https://w3c.github.io/webrtc-pc/#dom-rtcpeerconnection-removetrack

The error is consistent with Chrome (I think) when you try to do this:

const pc = new RTCPeerConnection();
pc.addStream(somelocalstream);
const sender = pc.getSenders()[0];
pc.removeTrack(sender);
pc.removeTrack(sender);

which throws the same error. Definetly something to fix but the transceiver model is a big chunk of work.