mm: swap: remove stale comment of swap_reclaim_full_clusters()

swap_reclaim_full_clusters() has no return value now, just remove the
stale comment which says swap_reclaim_full_clusters() wil return a bool
value.

Link: https://lkml.kernel.org/r/20250222160850.505274-7-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Kairui Song <ryncsn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>