Remove unused expressions (#6839)

Unused expressions are generally a mistake, as they don't do anything.
The exceptions to this rule (short-circuit expressions and ternary
expressions) have been allowed.

The `webrtc-adapter` was previously ignored by eslint because it has a
side-effect upon being imported. I removed the local variable instead,
which should preserve the same side-effect without making eslint
complain.

.eslintrc

@@ -133,6 +133,7 @@
     "no-unneeded-ternary": [2, { "defaultAssignment": false }],
     "no-unreachable": 2,
     "no-unsafe-finally": 2,
+    "no-unused-expressions": ["error", { "allowShortCircuit" : true, "allowTernary": true }],
     "no-unused-vars": [2, { "vars": "all", "args": "all", "argsIgnorePattern": "[_]+" }],
     "no-use-before-define": [2, { "functions": false }],
     "no-useless-call": 2,

ui/app/components/app/modals/qr-scanner/qr-scanner.component.js

@@ -1,7 +1,7 @@
 import React, { Component } from 'react'
 import PropTypes from 'prop-types'
 import { BrowserQRCodeReader } from '@zxing/library'
-import adapter from 'webrtc-adapter' // eslint-disable-line import/no-nodejs-modules, no-unused-vars
+import 'webrtc-adapter'
 import Spinner from '../../../ui/spinner'
 import WebcamUtils from '../../../../../lib/webcam-utils'
 import PageContainerFooter from '../../../ui/page-container/page-container-footer/page-container-footer.component'

ui/app/pages/home/home.container.js

@@ -3,7 +3,7 @@ import { compose } from 'recompose'
 import { connect } from 'react-redux'
 import { withRouter } from 'react-router-dom'
 import { unconfirmedTransactionsCountSelector } from '../../selectors/confirm-transaction'
-``
+
 const mapStateToProps = state => {
   const { metamask, appState } = state
   const {

ui/app/store/actions.js

@@ -1476,7 +1476,9 @@ function cancelAllTx (txsData) {
     txsData.forEach((txData, i) => {
       background.cancelTransaction(txData.id, () => {
         dispatch(actions.completedTx(txData.id))
-        i === txsData.length - 1 ? dispatch(actions.goHome()) : null
+        if (i === txsData.length - 1) {
+          dispatch(actions.goHome())
+        }
       })
     })
   }
@@ -2394,18 +2396,21 @@ function reshowQrCode (data, coin) {
   }
 }
 
-function shapeShiftRequest (query, options, cb) {
+function shapeShiftRequest (query, options = {}, cb) {
   var queryResponse, method
-  !options ? options = {} : null
   options.method ? method = options.method : method = 'GET'
 
   var requestListner = function () {
     try {
       queryResponse = JSON.parse(this.responseText)
-      cb ? cb(queryResponse) : null
+      if (cb) {
+        cb(queryResponse)
+      }
       return queryResponse
     } catch (e) {
-      cb ? cb({error: e}) : null
+      if (cb) {
+        cb({error: e})
+      }
       return e
     }
   }