Correct, there is no more calibration in 2.0 so there is no more calibration callback. Take a look at the OEEventsObserver header, docs or sample app to see the current delegate methods for OEEventsObserver – there should be one that is suitable.
Speaking in terms of the new architecture, I wouldn’t recommend starting the engine and immediately suspending it as a method of “priming” the engine so it was (sort of) ready to go whenever the user wanted to speak to the app. This was never a safe approach for recognition quality since it meant that the calibration would be for a different timeframe than when speech was actually allowed to enter the system and it also would probably result in clipped speech, but now it really has no upside since without having to wait for calibration, starting the engine is fast enough to just go ahead and start it when you want to start listening.