nixos/fwupd: disable test plugins implicitly

invalid test was introduced in https://github.com/fwupd/fwupd/commit/297d1598ef0739dc27c6cc884697bfd2ca03f2f5
and it is disabled in the shipped daemon.conf.

I forgot to reflect that in the module, which caused the daemon to print the following on start-up:

    FuEngine             invalid has incorrect built version invalid

and the command to warn:

    WARNING: The daemon has loaded 3rd party code and is no longer supported by the upstream developers!

To reduce the change of this happening in the future, I moved the list of default disabled plug-ins to the package expression.

I also set the value of the NixOS module option in the config section of the module instead of the default value used previously,
which will allow users to not care about these plug-ins.