Revert inadvertently pushed commit

This reverts commit 3a6114c025.
The actual solution is http://dev.drobilla.net/ticket/1085

gtk2_ardour/lv2_plugin_ui.cc

@@ -253,7 +253,6 @@ LV2PluginUI::lv2ui_instantiate(const std::string& title)
 		_ardour_buttons_box.show_all();
 
 		_gui_widget = Gtk::manage((container = new Gtk::Alignment()));
-		container->set (.5, .5, 0, 0);
 		pack_start(*_gui_widget, true, true);
 		_gui_widget->show();