Remove unused header styles

[tynandebold]

Description

Resolves #79

Development notes

I've removed the styles we weren't using.

Checklist

• [ ] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [ ] Added tests to cover my changes, where applicable

[netlify[bot]]

✅ Deploy Preview for kedro-website ready!

Name	Link
🔨 Latest commit	b6286f3c20897c201de46c384537c2c83282e02d
🔍 Latest deploy log	https://app.netlify.com/sites/kedro-website/deploys/64a47871578fdf0008b6a41f
😎 Deploy Preview	https://deploy-preview-150--kedro-website.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 configuration.