We do not have any way to reliably identify system apps and they can
easily lie about their ID. So it does not make much sense to give users
the illusion that they can control apps' access to their location.
Moreover, recently we ran into a bunch of annoying and hard to solve
issues related to authorization of system apps and we ended up with lots
of angry users.

Also we might also drop all agent/authorization in favour of an
appropriate Flatpak portal soon anyway: geoclue/geoclue#83

Fixes #76, #80.