ttk: fix LabeledScale and OptionMenu destroy() method (#3025)

bpo-31135: Call the parent destroy() method even if the used
attribute doesn't exist.

The LabeledScale.destroy() method now also explicitly clears label
and scale attributes to help the garbage collector to destroy all
widgets.

Lib/tkinter/ttk.py

@@ -1543,11 +1543,12 @@ class LabeledScale(Frame):
         try:
             self._variable.trace_vdelete('w', self.__tracecb)
         except AttributeError:
-            # widget has been destroyed already
             pass
         else:
             del self._variable
-            Frame.destroy(self)
+        super().destroy()
+        self.label = None
+        self.scale = None
 
 
     def _adjust(self, *args):
@@ -1644,5 +1645,8 @@ class OptionMenu(Menubutton):
 
     def destroy(self):
         """Destroy this widget and its associated variable."""
-        del self._variable
-        Menubutton.destroy(self)
+        try:
+            del self._variable
+        except AttributeError:
+            pass
+        super().destroy()