Remove dead helper code

[arjunkomath]

Summary

• remove unused helper exports and supporting dead constants/types
• drop stale tests that only covered removed test-only helpers
• keep remaining member role tests focused on used invite validation

Verification

• pnpm exec tsc --noEmit
• pnpm test

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 28e7b34.}