calendar: Launch the calendar server with DBus autostart

The supposed reason for launching the calendar server in a peculiar
way was so that the process would be killed when the Shell was killed,
but that didn't actually work. Launch the calendar server through auto-start,
and persist all throughout the session.

https://bugzilla.gnome.org/show_bug.cgi?id=683156

js/ui/main.js

@@ -80,10 +80,6 @@ let _overridesSettings = null;
 let background = null;
 
 function createUserSession() {
-    // Load the calendar server. Note that we are careful about
-    // not loading any events until the user presses the clock
-    global.launch_calendar_server();
-
     telepathyClient = new TelepathyClient.Client();
     automountManager = new AutomountManager.AutomountManager();
     autorunManager = new AutorunManager.AutorunManager();