memcg-v1: remove charge move code

The memcg-v1 charge move feature has been deprecated completely and let's
remove the relevant code as well.

Link: https://lkml.kernel.org/r/20241025012304.2473312-3-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: shakeelb

include/linux/memcontrol.h

@@ -299,11 +299,6 @@ struct mem_cgroup {
 	/* For oom notifier event fd */
 	struct list_head oom_notify;
 
-	/*
-	 * Should we move charges of a task when a task is moved into this
-	 * mem_cgroup ? And what type of charges should we move ?
-	 */
-	unsigned long move_charge_at_immigrate;
 	/* taken only while moving_account > 0 */
 	spinlock_t move_lock;
 	unsigned long move_lock_flags;