authdns: move standard include from role to site.pp

There is no real standard in the tree about whether to include standard
from within the role class. For authdns specifically, it has been
pointed out that this doesn't allow to share the boxes with other
services that conflict with standard (e.g. ntp). Move the include out of
the way to make it clearer that it's possible and easy to do so.

Change-Id: Iba858d2a7d92f1f6fb228e3c0a048c1d4aff3b31