memcg: cleanup with !CONFIG_MEMCG_V1

Extern declarations have no definitions with !CONFIG_MEMCG_V1 and no
users, drop them altogether.

Link: https://lkml.kernel.org/r/20240909163223.3693529-1-mkoutny@suse.com
Link: https://lkml.kernel.org/r/20240909163223.3693529-2-mkoutny@suse.com


Signed-off-by: Michal Koutný <mkoutny@suse.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>