memcg-v1: no need for memcg locking for dirty tracking

During the era of memcg charge migration, the kernel has to be make
sure that the dirty stat updates do not race with the charge migration.
Otherwise it might update the dirty stats of the wrong memcg.  Now
with the memcg charge migration gone, there is no more race for dirty
stat updates and the previous locking can be removed.

Link: https://lkml.kernel.org/r/20241025012304.2473312-4-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>