[Cashtab] Use ecash-lib for HDNode

Summary:
Now that we use ecash-lib for singing and verifying msgs, this is the last place we are still using utxo-lib.

Use ecash-lib instead. Remove the utxo-lib dependency.

bundle size goes from 858.92kB -> 559.61 kB with this diff; about 35% less

Test Plan:
npm test

this diff is deployed at https://cashtab-local-dev.netlify.app/

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D17804