Removes one tag from a contact, addressed by contact id and tag name, without needing the contactTag association id that DELETE /contactTags/{id} requires. Pass the tag name in the tag query parameter. To remove by tag id instead, use DELETE /contacts/{id}/tags/{tagId}; exactly one of the two must be used per request. The tag definition itself is not deleted. Returns 404 if the contact does not exist, the tag name does not exist, or the tag is not applied to that contact. Names containing commas or line breaks fail with 400.