docs: remove configuration-files-new.md

[mdjermanovic]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[x] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Follow-up to #17840

Removes configuration-files-new.md so that configuration-files-new doesn't appear in the navigation because this document is no longer needed since its content has been integrated into other documents. Also, we'll redirect this URL to configuration-files (eslint/eslint.org#499).

What changes did you make? (Give an overview)

• Removed configuration-files-new.md
• Updated the order field in documents under "Configure ESLint" so that it goes 1-7.
• Fixed an error caused by docs: Switch to flat config by default #17840 (comment).

Is there anything you'd like reviewers to focus on?

[netlify]

✅ Deploy Preview for docs-eslint ready!

Name	Link
🔨 Latest commit	27bc2aa
🔍 Latest deploy log	https://app.netlify.com/sites/docs-eslint/deploys/658bfd535352490008a2d4d0
😎 Deploy Preview	https://deploy-preview-17907--docs-eslint.netlify.app/extend/custom-rule-tutorial
📱 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.