Improved rendering when deleting an option from object's overrides.

Replaced the single column icon with an empty icon.
Will it break something? The single column added an ugly spacer
in front of non-editable combo boxes.

src/slic3r/GUI/GUI_ObjectSettings.cpp

@@ -10,6 +10,8 @@
 
 #include "I18N.hpp"
 
+#include <wx/wupdlock.h>
+
 namespace Slic3r
 {
 namespace GUI
@@ -84,6 +86,7 @@ void ObjectSettings::update_settings_list()
 			btn->Bind(wxEVT_BUTTON, [opt_key, config, this](wxEvent &event) {
 				config->erase(opt_key);
                 wxTheApp->CallAfter([this]() { 
+                    wxWindowUpdateLocker noUpdates(m_parent);
                     update_settings_list(); 
                     m_parent->Layout(); 
                 });