Remove staging test variant
Remove staging test variant

 ## Summary
Remove test variants for preview/staging required to release https://github.com/alphagov/digitalmarketplace-briefs-frontend/commit/b6b0ac571818f6b2dcf58db44df67234e7292ce6

alphagov/digitalmarketplace-functional-tests,alphagov/digitalmarketplace-functional-tests,alphagov/digitalmarketplace-functional-tests