BufferQueueProducer: Call onBuffersReleased() in detachNextBuffer

Like detachBuffer(), detachNextBuffer() needs to inform the consumer,
who generally has a cache of buffer items, that a buffer is no longer
owned by the buffer queue.

Otherwise the consumer layer can leak the buffer reference until
consumer teardown/disconnect.

Test: Camera CTS is fine, using a camera app shows correct memory
  behavior
Bug: 62591036

Change-Id: I14c200d13e60dbbe21261343941f84fb786db117