Remove breadcrumbs overflow menu feature flag

[pksjce]

• Closes https://github.com/github/primer/issues/5122

Changelog

New

Changed

Removed

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[bot]]

🦋 Changeset detected

Latest commit: 858a265e190f556491117e19cab70e179eb92a6e

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

This PR includes changesets to release 3 packages

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions[bot]]

:wave: 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!

[Copilot]

@pksjce I've opened a new pull request, #7082, to work on those changes. Once the pull request is ready, I'll request review from you.

[primer-integration[bot]]

:wave: Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/5654

[primer-integration[bot]]

🔴 ci completed with status failure.

[lesliecdubs]

@pksjce is this ready to get merged? Looks like it's been open and approved for a little while