samples/cgroup: rm unused MEMCG_EVENTS macro

samples/cgroup: rm unused MEMCG_EVENTS macro

MEMCG_EVENTS is never referenced in the code. Just remove it.

Link: https://lkml.kernel.org/r/20250903073100.2477-1-zhangjiao2@cmss.chinamobile.com
Signed-off-by: zhang jiao <zhangjiao2@cmss.chinamobile.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>