run_demo.py not tested, maybe remove

[lukpueh]

To test the demo automatically, e.g. on in-toto update, we extract and run the cli snippets in README.md and check the output with run_demo_md.py.

run_demo.py, on the other hand, was meant to verbosely walk through the demo, e.g. in a presentation (and to clean up the demo workbench).

However, run_demo.py must be synced with README manually, which is easily missed, because the script is not tested automatically.

I assume that the demo has become less relevant in presentations, but mostly used as in-toto getting started, for which the tested README should be sufficient.

Shall we just remove run_demo.py? Otherwise I recommend to also test it automatically.

[tonylturner]

FYI we do personally find run_demo.py helpful as we use this project in a supply chain course and some of my students are not very technical and benefit from just running this script.

[lukpueh]

Thanks for the feedback. That's great to hear. Let's keep it and add tests then.