Don't report event rejection errors via /send, since apparently thi…

…s is upsetting tests that don't expect that

roomserver/internal/input/input_events.go

@@ -175,7 +175,7 @@ func (r *Inputer) processRoomEvent(
 			"soft_fail": softfail,
 			"sender":    event.Sender(),
 		}).Debug("Stored rejected event")
-		return rejectionErr
+		return nil
 	}
 
 	switch input.Kind {