[cleanup] Remove unimplemented option
[cleanup] Remove unimplemented option

-overwrite option is not implemented yet.
Task T220305 is created for this feature.

Change-Id: I61cbaa0fb1084fd25e5b613c7a7de043fbb0a47c

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core