Add a function for deleting windows linked to main toolbar.

src/window_func.h

@@ -42,6 +42,7 @@ void InvalidateWindowClassesData(WindowClass cls, int data = 0, bool gui_scope =
 void DeleteNonVitalWindows();
 void DeleteAllNonVitalWindows();
 void DeleteConstructionWindows();
+void DeleteToolbarLinkedWindows();
 void HideVitalWindows();
 void ShowVitalWindows();