It is proposed to remove use self-contained challenges

[Denisthemalice]

In section 12.1 (Replay Attacks), the text states:

  -  use self-contained challenges while not storing the seen
     challenges.  This approach scales well, while only guaranteeing
     freshness, but no replay protection within the limited time-
     window chosen by the Authorization Server.

As this technique does not provide replay protection within the limited time-window, it should not be mentioned.