kmsan: fix a stale comment in kmsan_save_stack_with_flags()

After commit 446ec838 ("mm/page_alloc: use might_alloc()") and commit
84172f4b

 ("mm/page_alloc: combine __alloc_pages and
__alloc_pages_nodemask"), the comment is no longer accurate.  Flag
'__GFP_DIRECT_RECLAIM' is clear enough on its own, so remove the comment
rather than update it.

Link: https://lkml.kernel.org/r/20230327034149.942-1-thunder.leizhen@huawei.com
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>