refactor: [M3-7736] - Clean up regionDropdown feature flag

[bnussman-akamai]

Description 📝

In production, regionDropdown has been enabled for the last two years and has not changed. I think we can safely remove this flag from the codebase. 🧹

Preview 📷

How to test 🧪

• Go to http://localhost:3000/account/billing/edit
• Verify Country and State are required
• Verify this drawer looks and functions the same locally as it does in production

As an Author I have considered 🤔

• 👀 Doing a self review
• ❔ Our contribution guidelines
• 🤏 Splitting feature into small PRs
• ➕ Adding a changeset
• 🧪 Providing/Improving test coverage
• 🔐 Removing all sensitive information from the code and PR description
• 🚩 Using a feature flag to protect the release
• 👣 Providing comprehensive reproduction steps
• 📑 Providing or updating our documentation
• 🕛 Scheduling a pair reviewing session
• 📱 Providing mobile support
• ♿ Providing accessibility support

[github-actions]

Coverage Report: ✅
Base Coverage: 81.18%
Current Coverage: 81.18%

[bnussman-akamai]

billing/billing-contact.spec.ts failure is related to parent child. This PR should be okay!

[abailly-akamai]

Thanks for the cleanup! Confirming the behavior is unchanged ✅

[mjac0bs]

Fields are still required, functionality unchanged. 🚢 🧹