Drop policyrcd-script-zg2 from depends and add it to conflicts instead.

Drop policyrcd-script-zg2 from depends and add it to conflicts instead.

policyrcd-script-zg2 installs a symlink for policy-rc.d using the
update-alternatives mechanism causing conflicts with dpkg-divert
(used within FAI).

Now just provide what policyrcd-script-zg2 does inside grml-policy-rc.d
itself.

While at it drop conflicts "grml-scripts (<= 0.7-37), grml-etc (<< 1.1.34)"
as they are very outdated and shouldn't be present anywhere anymore.