Removing matProps dataSchema

[john-science]

What is the change? Why is it being made?

The matProps/dataSchema package is not used by matProps, nor is it imported by anyone downstream.

But I have already found that it is mildly out-of-date, and kind of hard to keep track when and where to update it. It's NOT a bad package, but will cause a lot of hard-to-automate work over time. And, in the end, I think what people are really going to want is matProps documentation. It will be more helpful to people to read the docs to see what a matProps YAML file can look like; our users don't want to wade into the dataSchema format JSON file to try to figure it out themselves.

SCR Information

Change Type: trivial

One-Sentence Rationale: We should only include code that our users want.

One-line Impact on Requirements: NA

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.
• The documentation is still up-to-date in the doc folder.
• The code style follows good practices.
• The dependencies are still up-to-date in pyproject.toml.