C2BqPool: move pool data destruction out of lock

Move temporary pool data destructions while migrating buffers to new
IGBP out of lock. Dtor may trigger cancel, which requires lock.

Bug: 143147473
Test: atest CtsMediaTestCases -- --module-arg CtsMediaTestCases:size:small
Test: atest android.media.cts.AdaptivePlaybackTest
Change-Id: I215ac6b9fd00db27e2879761160004da432486ab