[CIFS] cleanup cifsd completion

Was a holdover from the old kernel_thread based cifsd
code. We needed to know that the thread had set the task variable
before proceeding. Now that kthread_run returns the new task, this
doesn't appear to be needed anymore.

As best I can tell, this sleep was intended to try to prevent
cifs_umount from freeing the cifsSesInfo struct before cifsd had
exited. Now that cifsd is using the kthread API, we know that
when kthread_stop returns that cifsd has exited, so I don't
think this is needed any longer.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Christop Hellwig <hch@infradead.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>