[Cashtab] Use token-server blacklist for agora

Summary:
We have a database blacklist live now that we can update without submitting diffs. Use that.

Fall back to local blacklist on error.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17036