Remove duplicated _optimize_trace and use core (#20394)
Summary:
The duplicated code of `_optimize_trace` in _pytorch_graph.py is used to bypass some optimization step which causes missing scope.
It seems that most of the problematic steps have been fixed recently. Standard models implemented in torchvision are visually inspected before the commit. However, the `+=` in https://github.com/pytorch/vision/blob/50d54a82d1479ffb6dd7469ed05fccdf290a1d84/torchvision/models/resnet.py#L63 will let https://github.com/pytorch/pytorch/blob/f4d9bfaa4dd983288518a310bb900756ee3c6046/torch/onnx/utils.py#L159 produce a bad result. It can be fixed by replacing it with `out += identity`. This also implies that `+=` has non-intuitive behavior.
cc orionr ezyang
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20394
Reviewed By: NarineK
Differential Revision: D15452204
Pulled By: orionr
fbshipit-source-id: eaa4c13f16551c78dc6419f1e22eb2c560af4cc5
