[Cashtab] Deprecate parsing encrypted msgs in tx history

Summary: Now that encrypted msg sending has been deprecated and disabled for over a month, stop parsing these txs in history. This allows us to remove 2 unused npm modules.

Test Plan: npm test, npm start and normal cashtab msgs render in tx history

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15062