Pius XI issued Crimen Solicitationis in 1922. Paul VI made the Pontifical Secret public in 1974 when it was gazetted as 'Secreta Continere'. John Paul II fiddled with it by placing a statute of limitations on it.
Erasing the Pontifical Secret from Canon Law is not complicated at all. The Pope is the Supreme  Legislator, not the Curia, so he can decide apart from any other authority to get rid of it. The Pope cling to it because it is one of the last means that the Vatican has of keeping bishops out of jail.