Simplify Vuex/Vue interaction in tests

spec/frontend/diffs/components/settings_dropdown_spec.js

 import { mount } from '@vue/test-utils';
-import Vue from 'vue';
-import Vuex from 'vuex';
+
+import { extendedWrapper } from 'helpers/vue_test_utils_helper';
 
 import SettingsDropdown from '~/diffs/components/settings_dropdown.vue';
 import { PARALLEL_DIFF_VIEW_TYPE, INLINE_DIFF_VIEW_TYPE } from '~/diffs/constants';
 import eventHub from '~/diffs/event_hub';
 
-import { extendedWrapper } from '../../__helpers__/vue_test_utils_helper';
-
 import createDiffsStore from '../create_diffs_store';
 
 describe('Diff settings dropdown component', () => {
@@ -15,8 +13,6 @@ describe('Diff settings dropdown component', () => {
   let vm;
   let store;
 
-  Vue.use(Vuex);
-
   function createComponent(extendStore = () => {}) {
     store = createDiffsStore();