[tg bot] deprecate unused and obsolete utils function

Summary:
T2972

Delete utils function that is now included in ecashaddrjs

This function is not yet used, so it also shouldn't be in the app yet.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13584