The highmem pages are supported since commit f1549cb5 ("mm/z3fold.c:
allow __GFP_HIGHMEM in z3fold_alloc").  Remove the residual comment.

Link: https://lkml.kernel.org/r/20220308134311.59086-3-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NVitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>