Emit redacted_event from the roomserver when redactions are validated (#1186)

* Emit redacted_event from the roomserver when redactions are validated

- Consume them in the currentstateserver and act accordingly.
- Add integration test for the roomserver to check that injecting
  `m.room.redaction` events result in `redacted_event` being emitted.

* Linting

* Ignore events that redact themselves

currentstateserver/storage/postgres/current_room_state_table.go

@@ -189,7 +189,6 @@ func (s *currentRoomStateStatements) SelectEventsWithEventIDs(
 		if err := rows.Scan(&eventBytes); err != nil {
 			return nil, err
 		}
-		// TODO: Handle redacted events
 		var ev gomatrixserverlib.HeaderedEvent
 		if err := json.Unmarshal(eventBytes, &ev); err != nil {
 			return nil, err