libceph: no need to call flush_workqueue() before destruction

destroy_workqueue() drains the workqueue before proceeding with
destruction.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/osd_client.c

@@ -5081,7 +5081,6 @@ int ceph_osdc_init(struct ceph_osd_client *osdc, struct ceph_client *client)
 
 void ceph_osdc_stop(struct ceph_osd_client *osdc)
 {
-	flush_workqueue(osdc->notify_wq);
 	destroy_workqueue(osdc->notify_wq);
 	cancel_delayed_work_sync(&osdc->timeout_work);
 	cancel_delayed_work_sync(&osdc->osds_timeout_work);