Package deprecated is used when we deprecated plugin. In plugin.cfg just go from
startup:github.com/mholt/caddy/startupshutdown
To:
startup:deprecated
And things should work as expected. This means starting CoreDNS will fail with an error. We can only
point to the release notes to details what next steps a user should take. I.e. there is no way to add this
to the error generated.