BBQ: Remove BufferFreedListener

If BBQ is destroyed without calling abandon, its BufferItemConsumer
will call onBufferFreed. Since BBQ registers itself as the
BufferFreedListener we end up trying to promote and destroy the
BBQ again. The BufferFreedListener is not used so as a simple fix,
we remove the listener.

Test: presubmit
Bug: 200246498
Change-Id: I7b2be265b3c09d691cc0c41b80c73067f9a8b84d