Revert update for dirty_ratio for memcg.

Revert update for dirty_ratio for memcg.

The flags added by commit db16d5ec1f87f17511599bc77857dd1662b5a22f
has no user now. We believe we'll use it soon but considering
patch reviewing, the change itself should be folded into incoming
set of "dirty ratio for memcg" patches.

So, it's better to drop this change from current mainline tree.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>