chore: Fix eslint-plugin-import newly reported linting errors hit by web-ext tests.

Author: rpl

tests/setup.js

@@ -1,5 +1,5 @@
-import chai from 'chai';
+import { use as chaiUse } from 'chai';
 import chaiAsPromised from 'chai-as-promised';
 
 // Enable chai-as-promised plugin.
-chai.use(chaiAsPromised);
+chaiUse(chaiAsPromised);

tests/unit/test-util/test.adb.js

@@ -1,6 +1,6 @@
 import EventEmitter from 'events';
 
-import chai from 'chai';
+import { assert } from 'chai';
 import { afterEach, describe, it } from 'mocha';
 import * as sinon from 'sinon';
 
@@ -36,8 +36,6 @@ ${fakeSocketFilePrefix} /dev/socket/mdns
 ${fakeSocketFilePrefix}  ${fakeRDPUnixSocketFile}
 `;
 
-const { assert } = chai;
-
 function getFakeADBKit({ adbClient = {}, adbkitUtil = {}, adbDevice = {} }) {
   const fakeTransfer = new EventEmitter();
   const adbUtilReadAllStub = sinon.stub();