These files are a template how to add a new nm-setting-* implementation.

We are not going to add new files to the deprecated libnm-util library,
hence a template for libnm-util is pointless.

libnm-core doesn't have a corresponding template file. Personally, I
don't think such a template are a great idea either, because

  - People are not aware that it exists. Hence, it's unused, badly
    maintained and quite possibly does not follow current best practice.
  - Just copy an actual settings implementation and start from there.
    That seems better to me than having a template.