Drop references to lists.a.o

Whilst lists.a.o is based on some code from Ponymail Foal, that service is run by a 3rd party, and does not run a vanilla version of the code, (even after allowing for necessary authentication changes).

Fixes and improvements to PonyMail are not guaranteed to be taken up by the providers of the lists.a.o service, which is subject to an agreement with ASF Infrastructure.

As such, most of the references are confusing, misleading or incorrect, and I think they should be removed.

Search the repository for `lists.a.o` and review each reference in context, since the issue does not name specific files. Remove references that are confusing, misleading, or incorrect, then verify that the remaining references accurately describe the project.

Written by the indexing model from the issue text.