[e.cash] Remove ecash-script from build page

Summary: This library will be deprecated. ecash-lib does it better and integrates better with chronik and other tools. ecash-script is still around bc some work to do in removing it from existing bitcoin-abc apps, but it is not recommended for new devs to use.

Test Plan: preview site, confirm link is gone

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16892