[marlin] Use getTxAmounts() from ecash-wallet to compute the transaction amount

Summary:
Kill some ecash-lib dependencies, simplify the code, and make it ready for HD wallet support.

Depends on D19403.

Test Plan:

pnpm test

Check the transaction history page still works the same.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D19404