systemd: simplify unit file

Avoid setting up the Alias rule, which was a helper to let us 'disable' the
systemd service including dbus-activations. Without the Alias, 'disable' will
still let starting ModemManager through dbus-activation. If you really want to
fully disallow starting MM also through dbus-activation, you should 'mask' and
'unmask' the service.

E.g.:
 $ sudo systemctl mask ModemManager
ln -s '/dev/null' '/etc/systemd/system/ModemManager.service'

 $ sudo mmcli -L
error: couldn't find the ModemManager process in the bus

 $ sudo systemctl unmask ModemManager
rm '/etc/systemd/system/ModemManager.service'

 $ sudo mmcli -L
No modems were found

https://bugzilla.gnome.org/show_bug.cgi?id=701229

.gitignore

@@ -25,8 +25,6 @@ libtool
 *.tar.bz2
 *.pyc
 *.dirstamp
-org.freedesktop.ModemManager.service
-org.freedesktop.ModemManager.conf
 callouts/mm-modem-probe
 test/lsudev
 

data/Makefile.am

@@ -33,17 +33,10 @@ endif
 
 # DBus Activation file
 dbusactivationdir = $(datadir)/dbus-1/system-services
+dbusactivation_in_files = org.freedesktop.ModemManager1.service.in
+org.freedesktop.ModemManager1.service: org.freedesktop.ModemManager1.service.in
+	$(edit) $< >$@
 dbusactivation_DATA = org.freedesktop.ModemManager1.service
-dbusactivation_in_files_systemd = org.freedesktop.ModemManager1.service.systemd.in
-dbusactivation_in_files_nosystemd = org.freedesktop.ModemManager1.service.nosystemd.in
-if HAVE_SYSTEMD
-org.freedesktop.ModemManager1.service: org.freedesktop.ModemManager1.service.systemd.in
-	$(edit) $< >$@
-else
-org.freedesktop.ModemManager1.service: org.freedesktop.ModemManager1.service.nosystemd.in
-	$(edit) $< >$@
-endif
-
 
 # Icon
 icondir=${datadir}/icons/hicolor/22x22/apps

data/ModemManager.service.in

@@ -10,4 +10,3 @@ StandardError=null
 
 [Install]
 WantedBy=multi-user.target
-Alias=dbus-org.freedesktop.ModemManager1.service

data/org.freedesktop.ModemManager1.service.in

@@ -2,3 +2,4 @@
 Name=org.freedesktop.ModemManager1
 Exec=@sbindir@/ModemManager
 User=root
+SystemdService=ModemManager.service

data/org.freedesktop.ModemManager1.service.systemd.in

@@ -1,11 +0,0 @@
-# This D-Bus service activation file is only for systemd support since
-# an auto-activated ModemManager would be quite surprising for those people
-# who have MM installed but turned off.  Thus the Exec path available to
-# D-Bus is /bin/false, but systemd knows the real Exec path due to the MM
-# systemd .service file.
-
-[D-BUS Service]
-Name=org.freedesktop.ModemManager1
-Exec=/bin/false
-User=root
-SystemdService=dbus-org.freedesktop.ModemManager1.service