Also if I simply remove the wicked package, that fixpersistentutilities page does not show anything for wicked in the global site manager. But if I view that locally on a site I am trying to migrate, I get "AttributeError: type object 'IFieldValueSetter' has no attribute 'iro'" like I mentioned above.
My guess is that at some point wicked used to register this locally and later changed it to a global setting. Perhaps the zope architecture ended up working in such a way that it would fall back to the global registration, and you could then unregister it from the global site manager, but if you didn't have the global registration to begin with it would just say the local adapter is invalid? I can't confirm this.