mm: remove PageWaiters, PageSetWaiters and PageClearWaiters

All callers have been converted to use folios.  This was the only user of
PF_ONLY_HEAD, so remove that too.

Link: https://lkml.kernel.org/r/20240227192337.757313-3-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>