This does two things:
* Allows new users of the library to see only the supported symbols
* Allows us to ensure we're not using deprecated API internally
I can also use this in gnome-software in CI to make sure we're not using
deprecated API too. I don't think we're ready for a soname bump so we have to
hang on to the deprecated code for now.
Add the concept of 'remotes' that can dropped into /etc and used as firmware
metadata sources. This may be desirable when firmware is only accessable with
a valid support contract or from behind a VPN.