on("stream") event should receive a unique MediaStream from a peer

[baptisteArno]

on("stream") event currently receives 2 MediaStream objects from a unique peer. Both of these streams contain the audio and video tracks. We should only receive the MediaStream once.

[TbreezyF]

You do have the MediaStream object sent once. The MediaStream however contains two tracks of type MediaStreamTrack. An audio and a video track

[afrokick]

Because we fire on('stream') when peerConnection.ontrack called, so it called twice per one MediaStream with two tracks.

https://github.com/peers/peerjs/blob/master/lib/negotiator.ts#L145-L154