[ecash-herald] Remove toLowerCase by using latest ecashaddrjs

Summary: chronik-client only accepts address type in lowercase, i.e. p2sh or p2pkh. Latest version of ecashaddrjs returns these values, so the toLowerCase() shim can be dropped.

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14171