Remove or upgrade stale @testing-library dependencies

[lmken]

Summary

All 4 React projects include @testing-library/react (13.4.0), @testing-library/jest-dom (5.17.0), and @testing-library/user-event (13.5.0). These are 3 major versions behind the latest (@testing-library/react is now at 16.3.2).

However, there are no actual test files in any of the projects — these dependencies appear to be unused scaffolding from Create React App.

Affected Packages

• moonpay-react-buy/package.json
• moonpay-react-sell/package.json
• moonpay-react-sell-oninitiatedeposit/react-widget-integration/package.json
• moonpay-react-sell-oninitiatedeposit/hosted-wallet-page/package.json

Options

1. Remove them entirely — no tests exist, removes unnecessary bloat (recommended)
2. Upgrade to latest — if tests are planned in the near future

Acceptance Criteria

• Decide whether to remove or upgrade
• If removing: delete all three @testing-library/* deps from all 4 React projects
• If upgrading: bump to latest versions, note that @testing-library/react 16+ requires @testing-library/dom as a peer dep
• npm install completes without errors