ref(JitsiConference): allow only 1 track per media type
ref(JitsiConference): allow only 1 track per media type

Only one audio or video track is correctly supported by lib-jitsi-meet.
This is an attempt to mitigate an issue reported by the community
where the user's audio is played in the conference even though the UI
shows the user as muted.

jitsi/lib-jitsi-meet,jitsi/lib-jitsi-meet