Your LISTSERV postmaster has to remove the list for you, but instead I
would actually recommend setting

* Subscription= Closed

in the list header and then setting up a SUB_CLOSED template form in your
listname.MAILTPL file that explains that the list is closed forever, amen,
or whatever you want to say.  This way people won't just get a "No such
list" message back from LISTSERV when trying to subscribe, and you won't
get any mail from LISTSERV about it.  You don't want to use the default
SUB_CLOSED template form since it says to contact the list owner for more
information.  A sample SUB_CLOSED might be something like this:

>>> SUB_CLOSED &LISTNAME is closed.
The &LISTNAME list has been closed since 19 February 1996.  Please inform
whoever maintains the site where you found this address that they should
update their information to reflect this fact.

which I actually use for a list that I closed down then but that I still
get mail about :(  Anyway, note that SUB_CLOSED is a linear template and
can't accept template formatting commands, so whatever you say you have
to say it in one paragraph.

Nathan