[Cashtab] Use correct type for comparison to dustSats
Summary:
currency.dustSats is a number, 550
remainder is a BigNumber
Both should be a BigNumber to use the gte comparison
Test Plan: npm start, send etoken txs, confirm you get a change output unless change would be dust
Reviewers: #bitcoin_abc, emack
Reviewed By: #bitcoin_abc, emack
Differential Revision: https://reviews.bitcoinabc.org/D11930