Removes one tag from a contact, addressed by contact id and tag id, without needing the contactTag association id that DELETE /contactTags/{id} requires. To remove by tag name instead, use DELETE /contacts/{contactId}/tags with the tag query parameter. The tag definition itself is not deleted. Returns 404 if the contact does not exist, the tag does not exist, or the tag is not applied to that contact. A tag id that is not a positive integer, or a request that also passes the tag query parameter, fails with 400.