block: simplify block_FifoRelease

Since the FIFO is being destroyed, there is no need to lock and to
update the FIFO internal state.

src/misc/block.c

@@ -550,7 +550,7 @@ block_fifo_t *block_FifoNew( void )
  */
 void block_FifoRelease( block_fifo_t *p_fifo )
 {
-    block_FifoEmpty( p_fifo );
+    block_ChainRelease( p_fifo->p_first );
     vlc_cond_destroy( &p_fifo->wait_room );
     vlc_cond_destroy( &p_fifo->wait );
     vlc_mutex_destroy( &p_fifo->lock );