Revert "Merge branch 'design-principles'"

This reverts commit ed1e9363317f26524b62efe81d9739730b4f4c53, reversing
changes made to 8cdde7a970fb9f10042f88f824613b3d29d6f476.

New SEO page needs linking and images adding before this can go live.
Since the application is being deployed to production today as part of
the service manual release, backing this out for now.