[e.cash] Tighten up wording on core-tech page

Summary: Remove obsolete and irrelevant portions

Test Plan: Ran it locally, looks fine

Reviewers: #bitcoin_abc, Fabien, bytesofman

Reviewed By: #bitcoin_abc, Fabien, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D15800