Remove python_new_version feature flag and irrelevant code

[amazimbe]

What are you trying to accomplish?

Remove a feature flag and code that is no longer needed.

The feature flag was added in this PR to ensure the new python version changes could be turned off easily if necessary.

It also removes old code from the previous implementation that is no longer relevant e.g the old version regex.

Anything you want to highlight for special attention from reviewers?

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[jurre]

Seems this is removing both the feature flag and (some of) the old version code?

[amazimbe]

Seems this is removing both the feature flag and (some of) the old version code?

Yes, it also removes the old versioning code that's no longer applicable in the new version. It replaces the old regex with the new one, for example.