event properties in API responses and AS API duplicated as top-level field

[matrixbot]

This issue has been migrated from #7925.

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When calling the /messages endpoint (also /search, /context, etc) each event in the chunk will have a number of top-level properties that duplicate those within unsigned:

• age (see also: age logic for events is broken #8429)
• redacted_because
• replaces_state
• invite_room_state
• knock_room_state.
• prev_content (though this one was specced until MSC3442)
• user_id (duplicates sender)

These top-level properties are not a part of the spec.

(Edited by @richvdh to make the list of affected properties clear)