fs/ocfs2/super: remove deprecated create_singlethread_workqueue()

fs/ocfs2/super: remove deprecated create_singlethread_workqueue()

The workqueue "ocfs2_wq" queues multiple work items viz
&osb->la_enable_wq, &journal->j_recovery_work, &os->os_orphan_scan_work,
&osb->osb_truncate_log_wq which require strict execution ordering.  Hence,
an ordered dedicated workqueue has been used.

WQ_MEM_RECLAIM has been set to ensure forward progress under memory
pressure because the workqueue is being used on a memory reclaim path.

Link: http://lkml.kernel.org/r/66279de510a7f4cfc6e386d99b7e04b3f65fb11b.1472590094.git.bhaktipriya96@gmail.com
Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <joseph.qi@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>