As a followup from #8967, I think we should generate deprecation warnings using an approach like https://github.com/certbot/certbot/pull/6859/files#diff-e5eaf744409c293203b898ba9896da75689fd04ff5f1566c035940a5b195c257 for any code in certbot.display.util that is unused and/or we don't want to be part of our public API.