Rename xdg-app-session.service to the recommended name

Using the bus name as the name of the service file is mandatory
for system services, and recommended for session services.

Signed-off-by: Simon McVittie <smcv@debian.org>

session-helper/Makefile.am.inc

@@ -12,9 +12,9 @@ session-helper/xdg-app-resources.c: session-helper/xdg-app.gresource.xml $(resou
 	$(AM_V_GEN) $(GLIB_COMPILE_RESOURCES) $< \
 		--target=$@ --sourcedir=$(srcdir) --c-name _gtk --generate-source
 
-service_in_files += session-helper/xdg-app-session.service.in
-service_DATA += session-helper/xdg-app-session.service
-DISTCLEANFILES += session-helper/xdg-app-session.service
+service_in_files += session-helper/org.freedesktop.XdgApp.service.in
+service_DATA += session-helper/org.freedesktop.XdgApp.service
+DISTCLEANFILES += session-helper/org.freedesktop.XdgApp.service
 
 EXTRA_DIST += session-helper/xdg-app.gresource.xml