ci: remove styled-components migration report

[joshblack]

Remove the report for styled-components now that it's complete! 🥳

[changeset-bot]

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Latest commit: 963083b

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[Copilot]

Pull Request Overview

This PR removes the completed styled-components migration tracking from the CI workflow, along with some cleanup to simplify the remaining migration status jobs.

• Removes the entire styled-components job that tracked the styled-components to CSS Modules migration
• Simplifies run commands from multi-line to single-line format
• Removes the --experimental-strip-types Node.js flag from TypeScript script execution
• Removes explicit "Set up Node.js" step names

[joshblack]

Confirmed that the workflow works by running workflow_dispatch which created this run: https://github.com/primer/react/actions/runs/19519131782

[liuliu-dev]

🧹 ✨