Remove compatibility for GTK+-2.0

While the Meego developers agreed to switching mutter to GTK+-3.0
unconditionally a while ago, Canonical used a GTK+-2.0 build for their
Unity project. As Canonical now announced a switch to compiz as their
window manager, there is no longer a reason to maintain GTK+-2.0
compatibility.

https://bugzilla.gnome.org/show_bug.cgi?id=633133

src/core/window-props.c

@@ -442,7 +442,7 @@ set_title_text (MetaWindow  *window,
       XDeleteProperty (window->display->xdisplay,
                        window->xwindow,
                        atom);
-      meta_error_trap_pop (window->display, FALSE);
+      meta_error_trap_pop (window->display);
     }
 
   return modified;