chore(vscode): remove `eslint.experimental.useFlatConfig`

[shinGangan]

🔗 Linked issue

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [x] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

eslint.experimental.useFlatConfig has been deprecated in vscode-eslint v3.0.5. Flat Config is enabled by default in ESLint v9. So I removed the option.

• ref1: https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint
• ref2: https://eslint.org/docs/latest/use/configure/migration-guide#visual-studio-code-support

[shinGangan]

Hi @benjamincanac , thank you for always reviewing! 🔥