unset(group_key, group_id, prop, modifiers, callback) {
        const identifiers = {$group_key: group_key, $group_id: group_id};
        this._unset({identifiers, prop, modifiers, callback})
    }
groups.unset(group_key, group_id, prop, modifiers, callback)
        ---
        delete a property on a group profile

        usage:

        mixpanel.groups.unset('company', 'Acme Inc.', 'products');

        mixpanel.groups.unset('company', 'Acme Inc.', ['products', 'customer segments']);