revert: updating type-guards to use Zod parsing (PL-753)

[zhihil]

…e reliable runtime validation (PL-753) (#790)" (#806)"

This reverts commit b495d0e.

Fixes or implements PL-753

Brief description. What is this change?

Implementation details. How do you make this change?

Setup information

Deployment Notes

Related PRs

• https://github.com/voiceflow/XXXXXXXXX/pull/123

Checklist

• Breaking changes have been communicated, including:
  • New required environment variables
  • Renaming of interfaces (API routes, request/response interface, etc)
• New environment variables have been deployed
• Appropriate tests have been written
  • Bug fixes are accompanied by an updated or new test
  • New features are accompanied by a new test

[linear]

PL-753 Update `@voiceflow/base-types` to handle null or undefined `payload`