mm: memcg: remove unused node/section info from pc->flags fix

mm: memcg: remove unused node/section info from pc->flags fix

Fix non-CONFIG_SPARSEMEM build, which failed with
mm/page_cgroup.c: In function `alloc_node_page_cgroup':
mm/page_cgroup.c:44: error: `start_pfn' undeclared (first use in this function)

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>