Remove deprecated AcceleratorConnector.parallel_devices

[DuYicong515]

Proposed refactor

Remove the unused property AcceleratorConnector.parallel_devices

https://github.com/PyTorchLightning/pytorch-lightning/blob/550d3a640d1bfeb731a16b2996d3160f0f7eb071/pytorch_lightning/trainer/connectors/accelerator_connector.py#L762-L764

Alternative

parallel_devices = getattr(Trainer.strategy, "parallel_devices", [Trainer.strategy.root_device])

Motivation

Remove unused accelerator_connector properties

AcceleratorConnector.parallel_devices was not used within PytorchLightning anymore and this property were not meant to be public. Trainer.strategy.parallel_devices is preferred compared to Trainer.accelerator_connector.parallel_devices

Pitch

Remove the property AcceleratorConnector.parallel_devices

Additional context

No other usage, should be a safe remove

cc @justusschock @awaelchli @rohitgr7 @four4fish

[kaushikb11]

@DuYicong515 Could you elaborate why we should remove it? It is used at multiple places in AcceleratorConnector.

[DuYicong515]

Hi @kaushikb11, Thanks for the comment!

There was no AcceleratorConnector.parallel_devices used in existing code base. Within accelerator_connector.py it's using a private variable _parallel_devices instead. Externally I think it's preferred to accessTrain.strategy.parallel_devices to access parallel_devices when using ParallelStrategy

The issue was intended to stop it being a public property, AcceleratorConnector._parallel_devices should be kept within accelrator_connector.py, while Trainer.strategy.parallel_devices is preferred compared to Trainer.accelerator_connector.parallel_devices

I also updated alternative + motivation section of the issue. Let me know if you have any further questions!