Revert "Pontentially save some time in
Scheduler::HandleIdleShutdown(). Only one tuner needs to be in use to
block shutdown, so if we find one then skip checking the others."

Not required, we were already doing this check. I blame code
blindness, I've been staring at it for so long I wasn't that I was no
longer seeing it.

This reverts commit e0f68241babfd4284cb03a7892d2f9f9f9b00cff.