ScheduleController still listens to PLAYBACK_TIME_UPDATED after reset, throws TypeError

[davemevans]

#1510 introduced a PLAYBACK_TIME_UPDATED event listener to handle quality change events, but this is not removed when ScheduleController is reset.

Subsequent events cause the callback to be called, but ScheduleController's state has been reset and a TypeError is thrown when attempting to access playbackController methods since this object is now null.

Steps to recreate: in ref player select any sample stream and wait for it to start, then click load again.

I'll issue a PR shortly.