mm/vmscan: remove obsolete comment in get_scan_count

Since commit 1431d4d1 ("mm: base LRU balancing on an explicit cost
model"), the relative value of each set of LRU lists is based on cost
model instead of rotated/scanned ratio.  Cleanup the relevant comment.

Link: https://lkml.kernel.org/r/20220409030245.61211-1-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>