Revert "Update redaction rules."

This reverts commit 203c107e9e.

proposals/3289-rooms-v8.md

@@ -13,10 +13,3 @@ version may include them.
 Room version `8` upon being added to the specification shall be considered stable.
 No other room versions are affected by this MSC. Before room version `8` can enter
 the specification, MSC3083 needs to complete its final comment period.
-
-## Updated redaction rules
-
-Room version 8 shall update the redaction rules for the `m.room.join_rules` event.
-[Room version 1](https://spec.matrix.org/unstable/rooms/v1/#redactions) defines
-that only the `join_rule` key in the content object should be kept. Room version
-8 defines that both the `join_rule` and `allow` keys of the content shall be kept.