Pull request checklist

[x] The PR has a proper title. Use Semantic Commit Messages. (No more branch-name title please)
[x] Make sure this is ready to be merged into the relevant branch. Please don't create a PR and let it hang for a few days.
[x] Ensure you can run the codes you submitted succesfully. These submissions will be prioritized for review:

Introduce improvements in program execution speed;

Introduce improvements in synthesis quality;

Fix existing bugs reported by user feedback (or you met);

Introduce more convenient user operations.

PR type

This pull-requests fixes tools/export_onnx.py script – to be able to export .pth models to onnx in the console. It reuses the existing code