Improve Python code: address unused variables (#11049)

* Address F841 (unused variable).

* Reformat.

* Add changelog fragment.

* More cleanup.

* Remove trailing whitespace.

* Readd removed code as a comment with TODO.

plugins/modules/xml.py

@@ -920,7 +920,6 @@ def main():
     input_type = module.params["input_type"]
     print_match = module.params["print_match"]
     count = module.params["count"]
-    backup = module.params["backup"]
     strip_cdata_tags = module.params["strip_cdata_tags"]
     insertbefore = module.params["insertbefore"]
     insertafter = module.params["insertafter"]