417: Remove legacy Drupal and WP REST API code

[rpeterman-gp]

Blocked by #425 Closes #417

To Review

• [ ] Checkout Branch.
• [ ] Run yarn.
• [ ] Run yarn dev:start.
• [ ] Go to localhost:3000.

...then...

• [ ] Ensure app functions as expected.
• [ ] Run yarn build.
• [ ] Ensure app builds w/o errors.