Deprecate or remove the `none` role

[jahn-junior]

The none role doesn't provide any additional functionality over traditional rST/MyST comments.

Before we remove this role, we need to do an org-wide search to see there's a nontrivial amount of projects using the role. If no such projects exist, I think we can safely remove the role and release a new major version. If there are enough teams using the role for such a breaking change to be disruptive, we should instead log a notice that it will be removed in a future version.