Do not advertise .d snippets over main config file

Do not advertise .d snippets over main config file

For daemons which have a main configuration file, there's
little reason for the administrator to use configuration snippets.
They are useful for packagers which need to override settings, but
we shouldn't advertise that as the main way of configuring those
services.

https://bugs.freedesktop.org/show_bug.cgi?id=89397