[ONNX] Remove aten parameter (#61652) (#62759)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62759
* remove aten argument in export()
* add export_to_pretty_string default value OperatorExportTypes.ONNX
* add DPYTORCH_ONNX_CAFFE2_BUNDLE description
Test Plan: Imported from OSS
Reviewed By: SplitInfinity
Differential Revision: D30349062
Pulled By: msaroufim
fbshipit-source-id: d9738f3aa8b80eac54548d0b9494f9f1e544f20f
Co-authored-by: Gary Miguel <garymiguel@microsoft.com>
