Take a tag off a subscriber

Removes this subscriber from this segment. Needs audience: write.

A tag decides what a person can read, so taking one off revokes this person's access to every article that segment was addressed to, with effect from the next page they load.

Removing a tag the subscriber does not hold succeeds, changes nothing and publishes no event.

Works on a retired tag, where applying one does not: taking a tag off can only ever narrow what somebody can read.

Publishes subscriber.tagged with direction: removed, unless the subscriber did not hold the tag.