Task description

as part of #10484, we are deprecating some sizable modules which will no longer need to be public due to certbot-apache & certbot-nginx's move into certbot's private code. in doing this, @bmw mentioned it'd be nice to also deprecate any certbot module which isn't currently being used by a plugin, which will substantially reduce our public-facing surface area and make maintenance and changes much easier.

this issue is for that latter change.