[Cashtab] [p3 remove BCH.getByteCount] Move calcFee to cashMethods
Summary:
T2730
Depends on D12377
Since calcFee no longer uses the BCH object, move it from useBCH.js to cashMethods.js
calcFee and getCashtabByteCount are also moved above the first call to calcFee in cashMethods.js. I don't think I had to do this...no errors...just superstition I guess.
Test Plan:
npm test and confirm unit tests still pass
npm start and confirm sending an XEC tx still works with expected fee behavior
Confirm sending an eToken tx still works with expected fee behavior
Reviewers: #bitcoin_abc, emack
Reviewed By: #bitcoin_abc, emack
Differential Revision: https://reviews.bitcoinabc.org/D12378