REF: ujson cleanups
- [ ] 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.

Cool nice work - merge on green Thanks @jbrockmendel  This breaks user code that relied on `pandas.io.json.loads`, I'm surprised this went in without a deprecation period or a mention in pandas 2.2's changelog. Is this not considered public API ? (the lack of any trailing underscore suggests it's not private) `pandas.io.json.loads` is not a public API. The public JSON methods are listed in https://pandas.pydata.org/docs/reference/io.html#json and the more general policy on what's public is stated in https://pandas.pydata.org/docs/reference/index.html#api-reference