hooks: be more consistent in only using active Ui entries

There is no UI to control or display the ui_active value for custom hooks, but
*if* they are inactive, they will be ignored in make_ui, and it will be
misleading and confusing to show them in the list of active custom hooks.

There *should* never be any inactive hooks entries, but let's be consistent in
handling the case *if* it should happen. (It happened for me while hacking
around.)