Chore(navlist): remove unneeded exports

[francinelucca]

Removes NavList.Group, NavList.GroupHeading styled wrappers, refactors NavList styled wrappers to use styled() convention instead of Box

Changelog

New

• Add missing isSlot checks to NavList

Changed

• Refactor NavList styled wrappers to use styled() instead of Box and to correctly forward the "as" prop

Removed

• styled wrappers for NavList.Group, NavList.GroupHeading
• tests that are no longer valid

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 2da51bf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Patch
@primer/styled-react	Patch

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/4796

[primer-integration]

🟢 ci completed with status success.

[siddharthkp]

Approved!

Clean up suggestion at a later stage: Because there is only instance of NavList with sx now, we could also update that instance and remove NavList from styled-react