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.
Merge pull request #1901 from alphagov/moah-fix-unpublishings

More unpublishing repairs