Fix group deleted
If a group that was configured to sync with Mailchimp is deleted in CiviCRM 2 issues arise:
- the sync fails, and the lock in the civivcrm_mailchimpsync_status remains as 'busy' which prevents any further sync
- the settings screen reports a Javascript error that precludes the screen from loading, hence the config cannot be edited
This PE solves these 2 issues independently.