mm/damon: remove obsolete comments of kdamond_stop

Since commit 0f91d133 ("mm/damon: simplify stop mechanism") delete
kdamond_stop and change to use kthread stop mechanism, these obsolete
comments should be removed accordingly.

Link: https://lkml.kernel.org/r/20220531020421.46849-1-zhouchengming@bytedance.com


Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>