[ENH] Undeprecate pivot_wider()

[derekpowell]

PR Description

Please describe the changes proposed in the pull request:

• Pull request to reverse deprecation of pivot_wider() as discussed and requested by @samukweku in [DEPR] deprecate pivot_wider #1263 and raised by me in issue reverse deprecation of pivot_wider() #1464.
• remove deprecation warnings from pivot_wider() and in docstring
• update tests xfail messages for test_expand_multiple_levels() and test_expand_multiple_levels_flatten_levels() -- tests seem to fail since pivot_wider() was deprecated but I can't find the source.

This PR resolves #1464

PR Checklist

Please ensure that you have done the following:

1. PR in from a fork off your branch. Do not PR from <your_username>:dev, but rather from <your_username>:<feature-branch_name>.

2. If you're not on the contributors list, add yourself to AUTHORS.md.

3. Add a line to CHANGELOG.md under the latest version header (i.e. the one that is "on deck") describing the contribution.
   • Do use some discretion here; if there are multiple PRs that are related, keep them in a single line.

Automatic checks

There will be automatic checks run on the PR. These include:

• Building a preview of the docs on Netlify
• Automatically linting the code
• Making sure the code is documented
• Making sure that all tests are passed
• Making sure that code coverage doesn't go down.

Relevant Reviewers

• @samukweku
• @ericmjl

[ericmjl]

I'm good to merge. Regarding the pre-commit hooks, @derekpowell I would usually ask that the PR submitter fix them, but these look unrelated to the changes you've put in, and since this is your first time, I'm happy to fix them in a later PR. @samukweku if you're good with the changes, please feel free to hit merge and lemme know -- I'll follow-up quickly with a few infra + CI changes that will make this easier for future devs.

[derekpowell]

Thanks @ericmjl @samukweku for your help and understanding!