Account for release callbacks when determing if sync is finished

The current code only considers sync complete when BBQ receives a commit
callback for a frame that's >= to the last acquired buffer. This is
because syncs always blocked anything that wasn't a sync so it was
guaranteed that the last acquired buffer was for a sync.

However, this doesn't work if we want to handle sync buffers that are
dropped. Those transactions may never get applied and therefore the
commit callback may never occur. In those cases, we still want to
consider the sync complete if the buffer is released since it's never
going to get applied.

Test: BLASTBufferQueueTest
Bug: 233625646
Change-Id: I43be3f8bfb41ef5d57e64ca118604fbbc7a81514