deletes a file
    filename being a value in the "id" key
    :param filename: <str>
    :param conn: <rethinkdb.DefaultConnection>
    :return: <dict>

def delete(filename, conn=None):
    """
    deletes a file
    filename being a value in the "id" key
    :param filename: <str>
    :param conn: <rethinkdb.DefaultConnection>
    :return: <dict>
    """
    return RBF.filter((r.row[PRIMARY_FIELD] == filename) | (r.row[PARENT_FIELD] == filename)).delete().run(conn)