Camera: Handle consumer side detach in BufferManager

- BufferQueue consumer may detach buffers, and BufferManager isn't
aware. Hook up onBufferRemoved callback so that BufferManager's internal
handoutBuffer and attachedBuffer counts can be updated when a buffer
is detached.
- Deleted some code that's not exercised any more.

Test: Camera CTS and burst capture.
Bug: 38238747
Change-Id: I6861da6e013fe5609907f807639c5d691c0c3af9