chore: specify yarn as package manager and remove unused dependency

[G-Rath]

Summary

With #1306 landed we now support any of the main package managers which includes for our internal plumbing, and since we're not specifying a package manager npm is being used by default which is highlighting a peer dependency conflict with react-transition-group - it turns out that we don't actually need this package anymore so it can just go, but I've also explicitly set the packageManager to be yarn since that is what was being used before.

Since this is also touching the package.json files, I figured it would be a good time to slip in running sort-package-json for consistency.

Pull Request checklist

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• Add/update test to cover these changes
• Update documentation
• Update CHANGELOG file