More unpublishing repairs

This converts a bunch of auto-redirecting unpublishings so that they do not
automatically redirect as they are not on GOV.UK. Instead, a splash page will be
shown. This is because the Publishing 2.0 stack does not support non-GOVUK
redirects at present, and whitehall Unpublishings are not valid without a GOVUK
alternative URL.

Follow up to this story: https://trello.com/c/nqvBhUVg/83-clean-up-existing-unpublishings