Bug: mailinglists mapping - private property handling is inconsistent

setup.py creates the mailinglists mapping with the properties:
description, list, name

However archiver.py creates entries using the properties:
description, list, name, private

Also edit-list.py stores entries using the properties:
description, list, name

If the private property is useful, then setup and edit-list.py should take account of it.

It's not clear if the private property is useful when applied to a list, as each message has a private property. It might be best to just drop the property in archiver.py.

Compare the mailinglists mapping written by setup.py, archiver.py, and edit-list.py, focusing on the inconsistent private property. Trace how list-level and message-level private values are used, then establish consistent handling across these entry points and verify that the resulting mappings match the intended behavior.

Written by the indexing model from the issue text.