[BE] set pretrained=False for onnx tests (#66312)
Summary:
Addresses this network risk mitigation mentioned in https://github.com/pytorch/pytorch/issues/65439#issuecomment-924627239.
I didn't include any mobile app/benchmarking changes because I think the pretrained matters there.
I ended up removing the changes in test_utils because those were sensitive to the pretrained variable.
I am saving the quantization test changes for another PR because they are currently disabled.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66312
Reviewed By: ejguan
Differential Revision: D31542992
Pulled By: janeyx99
fbshipit-source-id: 57b4f70247af25cc96c57abd9e689c34641672ff
