xrandr-indicator: don't reference a non existing property

I was planning to add global.stage_xwindow, back when this was
written for core. Then this became an extension, but the reference
staid there.
We could use clutter_x11_get_stage_window(), if that wasn't marked
(skip). For now, let's just 0 (it is correct anyway, as we want
the dialog to be system modal)

extensions/xrandr-indicator/extension.js

@@ -102,7 +102,7 @@ Indicator.prototype = {
                     output.set_rotation(bitmask);
                     try {
                         config.save();
-                        this._proxy.ApplyConfigurationRemote(global.stage_xwindow, event.get_time());
+                        this._proxy.ApplyConfigurationRemote(0, event.get_time());
                     } catch (e) {
                         log ('Could not save monitor configuration: ' + e);
                     }