Revert "Don’t serve admin assets from the CDN"
Revert "Don’t serve admin assets from the CDN"

The intention was to only affect admin pages, but in production-like
environments it also broke assets on the frontend.

For now, we'll live with the bug for respond.js and IE<9, until we have switched
the frontend to a finder.

This reverts commit 4396cc8e0c6477e9ca794ce7de03cd0c608ce85c.

alphagov/contacts-admin,alphagov/contacts-admin,alphagov/contacts-admin