application: Drop ignore_activation flag

Rather use gapplication service. This makes the flow similar to what
Chatty does and makes us hold/release rather than having an application
window.

It also allows us to drop the --daemon.

Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/760>

data/org.gnome.Calls-daemon.desktop.in

@@ -7,7 +7,7 @@ Keywords=Telephone;Call;Phone;Dial;Dialer;PSTN;
 # Translators: Do NOT translate or transliterate this text (this is an icon file name)!
 Icon=org.gnome.Calls
 TryExec=gnome-calls
-Exec=gnome-calls --daemon
+Exec=gnome-calls --gapplication-service
 Type=Application
 StartupNotify=true
 NoDisplay=true