Fixes the error when calling the DeleteButton of a RibbonButtonBar
File "..../python3.9/site-packages/wx/lib/agw/ribbon/buttonbar.py", line 614, in DeleteButton
self._buttons.pop(button)
TypeError: 'RibbonButtonBarButtonBase' object cannot be interpreted as an integer
Fixes the error when calling the DeleteButton of a RibbonButtonBar
Fixes #2511