revert wxwidgets control pool

src/slic3r/GUI/OptionsGroup.cpp

@@ -532,9 +532,6 @@ bool OptionsGroup::activate(std::function<void()> throw_if_canceled/* = [](){}*/
 
 	return true;
 }
-
-void free_window(wxWindow *win);
-
 // delete all controls from the option group
 void OptionsGroup::clear(bool destroy_custom_ctrl)
 {
@@ -563,10 +560,8 @@ void OptionsGroup::clear(bool destroy_custom_ctrl)
     if (custom_ctrl) {
         for (auto const &item : m_fields) {
             wxWindow* win = item.second.get()->getWindow();
-            if (win) {
-                free_window(win);
+            if (win)
                 win = nullptr;
-            }
         }
 		//BBS: custom_ctrl already destroyed from sizer->clear(), no need to destroy here anymore
 		if (destroy_custom_ctrl)