Remove manual management of the nonwg lists shown in the datatracker when mailman3 is integrated

[rjsparks]

Right now, the secretariat is manually maintaining the list of non-wg lists the datatracker displays.
This should become automated again when the datatracker is integrated with mailman3.
The endpoint may end up being entirely redesigned during that process - the requirement being captured here is that the maintenance of the result become as automated as possible.