mm/mmap: remove obsolete comment in ksys_mmap_pgoff

mm/mmap: remove obsolete comment in ksys_mmap_pgoff

RLIMIT_MEMLOCK is already reimplemented on top of ucounts now.  And
since commit c046d24b77e3 ("mm,hugetlb: remove mlock ulimit for
SHM_HUGETLB"), mlock ulimit for SHM_HUGETLB is further removed.

So we should remove this obsolete comment.

Link: https://lkml.kernel.org/r/20220309090623.13036-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>