Avoid deadlock in MessageQueue::onNewVsyncSchedule

It is hard to reproduce, but if the
VSyncDispatchTimerQueueEntry::callback is called at just the right time,
it will set mRunning to true, then wait on MessageQueue's mVsync.mutex,
which was already locked by onNewVsyncSchedule. When
onNewVsyncScheduleLocked destructs the old VSyncCallbackRegistration, it
needs to wait until mRunning is set back to false. But
VSyncDispatchTimerQueueEntry::callback cannot do that until
MessageQueue::vsyncCallback can lock the mutex.

Avoid this deadlock by moving the old VSyncCallbackRegistration's
destruction until after mVsync.mutex is released.

Bug: 276367387
Test: infeasible
Change-Id: I86e66df59c64e81c4aa721a25250697f61237488