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/workspace.c

@@ -765,7 +765,7 @@ set_active_space_hint (MetaScreen *screen)
                    screen->display->atom__NET_CURRENT_DESKTOP,
                    XA_CARDINAL,
                    32, PropModeReplace, (guchar*) data, 1);
-  meta_error_trap_pop (screen->display, FALSE);
+  meta_error_trap_pop (screen->display);
 }
 
 void