[Cashtab] [p2 remove BCH.getByteCount] Replace BCH.getByteCount in calcFee

Summary:
T2730

Depends on D12376

Replace the BCH method in the calcFee function. This means that BCH is no longer an input parameter to calcFee, so it is removed in all function calls.

Test Plan:
Review updated function and npm test. Note that the existing unit test for calcFee still passes.

grep -r calcFee web/cashtab/src. Confirm that all calls to calcFee have had the BCH parameter removed.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12377