[token-server] Replace references to ChronikClientNode with ChronikClient

Summary: Update token-server to use current nomenclature and not legacy ChronikClientNode

Test Plan: npm test, grep -r ChronikClientNode . and no output

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16654