mm: remove the unused zone->unaccepted_cleanup

Commit fefc075182 ("mm/page_alloc: fix race condition in unaccepted
memory handling") removed the zones_with_unaccepted_pages static key and
the work that decremented it, but left the work_struct behind in struct
zone.  Nothing uses it anymore, so let's remove it.

Link: https://lore.kernel.org/20260924191103.3475117-1-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Kairui Song <kasong@tencent.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>

include/linux/mmzone.h

@@ -1077,9 +1077,6 @@ struct zone {
 #ifdef CONFIG_UNACCEPTED_MEMORY
 	/* Pages to be accepted. All pages on the list are MAX_PAGE_ORDER */
 	struct list_head	unaccepted_pages;
-
-	/* To be called once the last page in the zone is accepted */
-	struct work_struct	unaccepted_cleanup;
 #endif
 
 	/* zone flags, see below */