Redacting an edited message only redacts original message but leaved edited one visible

[JochenFriedrich]

Steps to reproduce:

1. Submit a message
2. Edit the message
3. Delete (redact) the message

The edited message is still shown in legacy clients. If you turn on hidden events, you can also select the edited message and click on show source to view the message.

[tulir]

Duplicate of matrix-org/synapse#10111, which points to matrix-org/matrix-spec#1328