chore: clean up npm dependencies

[backflip]

This PR removes two unused dependencies and moves one "build dependency" from dependencies to devDependencies.

[netlify[bot]]

✅ Deploy Preview for accessibility-developer-guide ready!

Name	Link
🔨 Latest commit	4d33c58ef32e0d500fd648ee068af9f18a424c1c
🔍 Latest deploy log	https://app.netlify.com/sites/accessibility-developer-guide/deploys/64511872b4c5090008d5fdae
😎 Deploy Preview	https://deploy-preview-395--accessibility-developer-guide.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[christophdubach]

Site is built and served without errors, so PR is approved.