[chronik-client] Remove test dependency on reindexing node

Summary:
chronik-client makes live API calls during unit tests. This should be changed, but requires new py scripts to mock actual chronik instances and server responses.

In the meantime, this is a quick patch to remove test dependency on non-abc infra.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14801