session: Don't set XSMP restart

This made sense back in the day of stateless window managers,
but gnome-shell isn't.  gnome-session will handle gnome-shell
crashing, since it's a required component.

https://bugzilla.gnome.org/show_bug.cgi?id=644529

src/core/main.c

@@ -348,8 +348,6 @@ meta_finalize (void)
   if (display)
     meta_display_close (display,
                         CurrentTime); /* I doubt correct timestamps matter here */
-
-  meta_session_shutdown ();
 }
 
 static int sigterm_pipe_fds[2] = { -1, -1 };