memcg: remove inc/dec_lruvec_kmem_state helpers

memcg: remove inc/dec_lruvec_kmem_state helpers

The dec_lruvec_kmem_state helper is unused by any caller and can be safely
removed.  Meanwhile, the inc_lruvec_kmem_state helper is only referenced
by shadow_lru_isolate, retaining these two helpers is unnecessary.  This
patch removes both helper functions to eliminate redundant code.

Link: https://lkml.kernel.org/r/20251126020435.1511637-1-chenridong@huaweicloud.com
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Acked-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lu Jialin <lujialin4@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>