Fix onnx passes (#22319)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22319
The onnx pass replacing ints with Tensors produces an invalid JIT graph. It should only be called right before the onnx pass.
Also, it should only be called if we actually export to onnx.
Reviewed By: houseroad
Differential Revision: D16040374
fbshipit-source-id: e78849ee07850acd897fd9eba60b6401fdc4965b
