This allows grd handover service to be started even with network access
through a mobile device or when the network access is from Wi-Fi.

Clear members of GsdPrintNotificationsManager in stop()
to not throw "Cancel-Subscription client-error-not-found" error
due to cancelling subscription twice.

0bfc6081 introduced a bunch of
systemd-specific stuff that broke building without systemd. Guard all of
the relevant things.

(cherry picked from commit 4da55072f61bb9a276ca6a35f79ba6406ada47fd)

Remove an extraneous "that".