Simulate muted audio track publish on migration. (#1799)

Till now only video was using simulated publish when migrating on mute.
But, with `pauseUpstream() + replaceTrack(null)`, it is possible that
client does not send any data when muted.

I do not think there is a problem to do this (even when cleint is
actually using mute which sends silence frames).

pkg/rtc/participant.go

@@ -569,7 +569,7 @@ func (p *ParticipantImpl) handleMigrateMutedTrack() {
 		}
 
 		ti := pti.trackInfos[0]
-		if ti.Muted && ti.Type == livekit.TrackType_VIDEO {
+		if ti.Muted {
 			mt := p.addMigrateMutedTrack(cid, ti)
 			if mt != nil {
 				addedTracks = append(addedTracks, mt)