dm: remove flush_scheduled_work() during local_exit()

Commit acfe0ad7 ("dm: allocate a special workqueue for deferred
device removal") switched from using system workqueue to a single
workqueue local to DM.  But it didn't eliminate the call to
flush_scheduled_work() that was introduced purely for the benefit of
deferred device removal with commit 2c140a24 ("dm: allow remove to
be deferred").

Since DM core uses its own workqueue (and queue_work) there is no need
to call flush_scheduled_work() from local_exit().  local_exit()'s
destroy_workqueue(deferred_remove_workqueue) handles flushing work
started with queue_work().

Fixes: acfe0ad7 ("dm: allocate a special workqueue for deferred device removal")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm.c

@@ -233,7 +233,6 @@ static int __init local_init(void)
 
 static void local_exit(void)
 {
-	flush_scheduled_work();
 	destroy_workqueue(deferred_remove_workqueue);
 
 	unregister_blkdev(_major, _name);