mm: unexport folio_memcg_{,un}lock

Patch series "unexport memcg locking helpers".

Neither the old page-based nor the new folio-based memcg locking helpers
are used in modular code at all, so drop the exports.

This patch (of 2):

folio_memcg_{,un}lock are only used in built-in core mm code.

Link: https://lkml.kernel.org/r/20210820095815.445392-1-hch@lst.de
Link: https://lkml.kernel.org/r/20210820095815.445392-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Christoph Hellwig

mm/memcontrol.c

@@ -2058,7 +2058,6 @@ void folio_memcg_lock(struct folio *folio)
 	memcg->move_lock_task = current;
 	memcg->move_lock_flags = flags;
 }
-EXPORT_SYMBOL(folio_memcg_lock);
 
 void lock_page_memcg(struct page *page)
 {
@@ -2092,7 +2091,6 @@ void folio_memcg_unlock(struct folio *folio)
 {
 	__folio_memcg_unlock(folio_memcg(folio));
 }
-EXPORT_SYMBOL(folio_memcg_unlock);
 
 void unlock_page_memcg(struct page *page)
 {