R1:3a046384e97e

Drop the `metamta_mailinglist` table

Summary: We haven't seen any issues here, remove the table and schema spec.

Test Plan: Not yet tested.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14067