Remove incorrect localVue usage

localVue is required only with use method

spec/frontend/monitoring/components/charts/column_spec.js

-import { shallowMount, createLocalVue } from '@vue/test-utils';
+import { shallowMount } from '@vue/test-utils';
 import { GlColumnChart } from '@gitlab/ui/dist/charts';
 import ColumnChart from '~/monitoring/components/charts/column.vue';
 
-const localVue = createLocalVue();
-
 jest.mock('~/lib/utils/icon_utils', () => ({
   getSvgIconPathContent: jest.fn().mockResolvedValue('mockSvgPathContent'),
 }));
@@ -12,7 +10,7 @@ describe('Column component', () => {
   let columnChart;
 
   beforeEach(() => {
-    columnChart = shallowMount(localVue.extend(ColumnChart), {
+    columnChart = shallowMount(ColumnChart, {
       propsData: {
         graphData: {
           metrics: [
@@ -35,7 +33,6 @@ describe('Column component', () => {
         containerWidth: 100,
       },
       sync: false,
-      localVue,
     });
   });
 

spec/frontend/monitoring/components/charts/empty_chart_spec.js

-import { shallowMount, createLocalVue } from '@vue/test-utils';
+import { shallowMount } from '@vue/test-utils';
 import EmptyChart from '~/monitoring/components/charts/empty_chart.vue';
 
-const localVue = createLocalVue();
-
 describe('Empty Chart component', () => {
   let emptyChart;
   const graphTitle = 'Memory Usage';
 
   beforeEach(() => {
-    emptyChart = shallowMount(localVue.extend(EmptyChart), {
+    emptyChart = shallowMount(EmptyChart, {
       propsData: {
         graphTitle,
       },
       sync: false,
-      localVue,
     });
   });
 

spec/frontend/monitoring/components/charts/single_stat_spec.js

-import { shallowMount, createLocalVue } from '@vue/test-utils';
+import { shallowMount } from '@vue/test-utils';
 import SingleStatChart from '~/monitoring/components/charts/single_stat.vue';
 import { graphDataPrometheusQuery } from '../../mock_data';
 
-const localVue = createLocalVue();
-
 describe('Single Stat Chart component', () => {
   let singleStatChart;
 
   beforeEach(() => {
-    singleStatChart = shallowMount(localVue.extend(SingleStatChart), {
+    singleStatChart = shallowMount(SingleStatChart, {
       propsData: {
         graphData: graphDataPrometheusQuery,
       },
       sync: false,
-      localVue,
     });
   });