exofs: deprecate the commands pending counter

One leftover from the days of IBM's original code, is an SB counter
that counts in-flight asynchronous commands. And a piece of code that
waits for the counter to reach zero at unmount. I guess it might have
been needed then, cause of some reference missing or something.

I'm not removing it yet but am putting a warning message if ever this
counter triggers at unmount. If I'll never see it triggers or reported
I'll remove the counter for good.
(I had this print as a debug output for a long time and never had it
 trigger)
Signed-off-by: NBoaz Harrosh <bharrosh@panasas.com>

fs/exofs/super.c

@@ -409,6 +409,10 @@ static void exofs_put_super(struct super_block *sb)
 	for (num_pend = atomic_read(&sbi->s_curr_pending); num_pend > 0;
 	     num_pend = atomic_read(&sbi->s_curr_pending)) {
 		wait_queue_head_t wq;
+
+		printk(KERN_NOTICE "%s: !!Pending operations in flight. "
+		       "This is a BUG. please report to osd-dev@open-osd.org\n",
+		       __func__);
 		init_waitqueue_head(&wq);
 		wait_event_timeout(wq,
 				  (atomic_read(&sbi->s_curr_pending) == 0),