refactor: deprecate dead code

[JoLo90]

• Closes DOC: dead code and wrong parameter in _liujordan function description #2764, Many deprecations in standby #2767, Dead code #2768
• I am familiar with the contributing guidelines
• I attest that all AI-generated material has been vetted for accuracy and is in compliance with the pvlib license
• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

[cwhanse]

@JoLo90 I think we should consider each of these removals before bundling them all into one PR. Can you open a few more issues to discuss other removals?

[JoLo90]

I just separated the issues in #2764, #2767, #2768

[RDaxini]

Added a suggestion to the whatsnew. I can do a a more technical review later.
Note for future PRs though @JoLo90, please only tick off checklist items when complete. For example, a maintainer has not added any relevant labels or milestone to this PR yet so this should not have been ticked. I will do it now (so no need to remove the tick now). This will just help us organize the work more efficiently and ensure we don't miss anything.
Thanks again for your continued contributions by the way, these are appreciated.