mm: remove khugepaged double thp vmstat update with CONFIG_NUMA=n

Johannes noticed the vmstat update is already taken care of by
khugepaged_alloc_hugepage() internally.  The only places that are required
to update the vmstat are the callers of alloc_hugepage (callers of
khugepaged_alloc_hugepage aren't).

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>