CI: clean up wheel build workarounds now that Cython 3.1.0 is out
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

This simplifiers wheel builds for free-threaded CPython, which is useful in itself and I thought was a good idea before backporting the Windows cp313t wheel support to the 2.3.x branch, as just discussed at https://github.com/pandas-dev/pandas/pull/61249#issuecomment-2885514360.

This should have no changes in behavior, and mostly reverts the workarounds for unreleased Cython added initially in gh-60146. Other notes:
- Changes the `free-threaded-support` cibuildwheel setting to `enable`, because the former is now deprecated.
- This leaves the license concatenation behavior unchanged. Note that it's skipped on Windows, and happens on other platforms. This was added without any discussion in gh-60146. It looks inconsistent, but the bash invocation doesn't work on Windows so I'd like to leave it unchanged in this PR. A useful follow-up PR may be to remove the ad-hoc concatenation in favor of starting to use [PEP 639](https://peps.python.org/pep-0639/).

I ran the wheel builds on my fork before opening this PR, they're passing ([CI logs](https://github.com/rgommers/pandas/actions/runs/15060502913)).
Thanks @rgommers  Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
git checkout 2.3.x
git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
git cherry-pick -x -m1 17f0dd6233a881702b36a301f4b8dd82f7d9f9a8
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
git commit -am 'Backport PR #61446: CI: clean up wheel build workarounds now that Cython 3.1.0 is out'
```

4. Push to a named branch:

```
git push YOURFORK 2.3.x:auto-backport-of-pr-61446-on-2.3.x
```

5. Create a PR against branch 2.3.x, I would have named this PR:

> "Backport PR #61446 on branch 2.3.x (CI: clean up wheel build workarounds now that Cython 3.1.0 is out)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the `Still Needs Manual Backport` label once the PR gets merged.

If these instructions are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 Manual backport -> https://github.com/pandas-dev/pandas/pull/61752