Delete webhook.

def delete_webhook(webhook_id):
    """Delete webhook."""
    webhook = get_data_or_404('webhook', webhook_id)
    action = get_data_or_404('action', webhook['action_id'])
    project = get_data_or_404('project', action['project_id'])

    if project['owner_id'] != get_current_user_id():
        return jsonify(message='forbidden'), 403

    delete_instance('webhook', action['id'])

    return jsonify({})