[ecash-herald] Patch sync functions defined as async in utils unit test

Summary:
Depends on D14187

A lot of sync unit tests are defined as async since an API testing function was copy pasted as a template a long time ago. Patch it.

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14188