Fix the fixed_queue_try_remove_from_queue() internals

Calling fixed_queue_try_remove_from_queue() should update
queue->dequeue_sem and queue->enqueue_sem as appropriate.

Also:
 * Removed function fixed_queue_init() because it is not used
 * Added fixed_queue_test.cpp unit tests for fixed_queue
 * Updated some of the fixed_queue API description

Bug: 25973053

Change-Id: I3a0931f34fed34a2d60f82904601ef4157ee8ff9
4 files changed