DROP TABLE IF EXISTS acoustid_settings;
DROP TABLE IF EXISTS track_acoustid_lookups;
-- Looked-up ids go with the lookups; a tag id stays.
UPDATE tracks SET mbid = NULL WHERE mbid_source = 'acoustid';
ALTER TABLE tracks DROP CONSTRAINT IF EXISTS tracks_mbid_source_pair;
ALTER TABLE tracks DROP CONSTRAINT IF EXISTS tracks_mbid_source_check;
ALTER TABLE tracks DROP COLUMN IF EXISTS mbid_source;