[Cashtab] Standardize use of Promise.all in useBCH.js
[Cashtab] Standardize use of Promise.all in useBCH.js

Summary:
T2105

`useBCH.js` has inconsistent implementation of `Promise.all().` This is an artifact from Cashtab's original launch. Cashtab is either (1) calling `await <some async function` and then calling `Promise.all`, which isn't actually the intended behavior, or it is calling an async function without await and thus instantly calling a function (and then calling it again under `Promise.all`

This behavior "works" but is neither clean nor desirable.

This diff standardizes the use of `Promise.all` in all instances by wrapping the intended async function in a promise-return function. Variables are also renamed in a standard way.

Test Plan: `npm start`, send and receive txs, observe no change in app behavior

Reviewers: emack, #bitcoin_abc

Reviewed By: emack, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10775

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