[ecash-herald] Deprecate block-based daily msgs

Summary:
Daily summary messages handled by cron are working, sending to channel https://t.me/eCashEveryDay

Stop sending daily summaries based on blocks into the herald channel.

In this way we have a more public-facing daily summary channel, and a more dev/power-user-facing every-block channel.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16974