[alias-server] Deprecate custom log function

Summary:
T3060

This was useful in early testing to view detailed object data in the log. This isn't useful for the prod app. Causes additional complications in that JSON.stringify will render an empty object if the data is typed, e.g. an Error.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13812