Let's merge -admin and -discuss

[Martin Michlmayr <tbm@cyrius.com>]

We currently have 2 New Maintainer related mailing lists:

-admin for administrative stuff (AM reports, news for AMs)
-discuss for disussions about NM in general

Mails to the former list are also sent to the latter.

I don't think that makes sense.  -discuss doesn't make much sense on
its own since there is not much traffic, and -admin is a closed list
which doesn't make any sense since the mails are sent to -discuss
anyway (-admin is only an administrative burden to the FD who has to
subscribe new AMs to the closed list).

I thus suggest to merge those two lists, and make one open list.