Fix DrmOutput sometimes being freed with a pending pageflip, often when waking from sleep.

It is possible for updateOutputs to be called when a pageflip is pending.
Freeing a DrmOutput with a pending pageflip is not allowed (see ~DrmOutput assert - the page flip handler will be called on the freed memory, possibly leading to use-after-free).
This works around the problem by delaying the destruction with teardown().

BUG: 422460