[token-server] Remove dead code websocket handler

Summary:
token-server no longer uses a chronik websocket. the tests and calls were removed in the ecash-lib implementation diff, but neglected to remove this file.

ref D16555

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16632