Comment #9 on issue 3620 by [email protected]: Settings: OCompletion settings appear twice
http://code.google.com/p/pharo/issues/detail?id=3620
I don't think you'll be able to successfully push a change which would remove access to the preference in Squeak to the OCompletion repository.
Probably better to change the Settings Browser UI to not display settings defined in both ways (<systemsettings> and <preference:category:...> )twice.
