Deprecate csv geometry examples and their data

[beomki-yeo]

I don't think they are useful anymore in traccc.
I suggest to cleanup the README instructions, relavant data and I/O codes.
@krasznaa @stephenswat How do you think?

[stephenswat]

I think we still need the CSV data, but I agree that the CSV geometries can go.

[beomki-yeo]

Yeah I was meaning the csv geometries only and data generated with csv geometries

[krasznaa]

🤔 Let's talk about this today. As I've thought about this a fair amount wrt. #627. Removing the ability to read CSV geometry files is not going to get rid of nearly as much code as you might think. But it's easier if we discuss this in person...