Stop clearing page flags in vm_page_pqbatch_submit().

All existing callers guarantee that the page does not have a
pre-existing dequeue pending.  Thus, if the page is dequeued before
pqbatch_submit() acquires the page queue lock, we do not need to do
anything since vm_page_dequeue_complete() takes care of clearing all
page queue state flags for us.

With this change, vm_page_pqbatch_submit() has the nice property that it
does not directly modify any fields in the page structure.

Reviewed by:	alc, kib
Tested by:	pho (part of a larger change)
MFC after:	1 week
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D21372

sys/vm/vm_page.c

@@ -3174,7 +3174,6 @@ vm_page_pqbatch_submit(vm_page_t m, uint8_t queue)
 		    ("invalid queue transition for page %p", m));
 		KASSERT((m->aflags & PGA_ENQUEUED) == 0,
 		    ("page %p is enqueued with invalid queue index", m));
-		vm_page_aflag_clear(m, PGA_QUEUE_STATE_MASK);
 	}
 	vm_pagequeue_unlock(pq);
 	critical_exit();