refactor: remove unused constants and options

[BobbieGoede]

🔗 Linked issue

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [x] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Some cleanup, most of the constants were added while integrating vue-i18n-routing, and the default options are already applied as defaults on nuxtI18nOptions on module install.

📝 Checklist

• [ ] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.