parker: remove prefix6 and prefix4

This change removes the prefix4 and prefix6 attributes from the
site.conf. These do not make sense in the context of parker.

Packages that are usually used in parker do not use these anymore. Some
other packages do - you should not enable those :-)

With this change a ipv6 route to prefix_6 will no longer be set on
br-client. Systems that already have this route will keep it.

With this change the (not working) redirect in the http status page has
been removed. We should consider to add this later on.