Remove OnDemandScansApp component

Removes the OnDemandScansApp component which used to be the entry point
for On-demand scans but was eventually replaced with OnDemandScansForm.

ee/app/assets/javascripts/on_demand_scans/components/on_demand_scans_app.vue

-<script>
-import OnDemandScansForm from './on_demand_scans_form.vue';
-
-export default {
-  name: 'OnDemandScansApp',
-  components: {
-    OnDemandScansForm,
-  },
-  props: {
-    helpPagePath: {
-      type: String,
-      required: true,
-    },
-    projectPath: {
-      type: String,
-      required: true,
-    },
-    defaultBranch: {
-      type: String,
-      required: false,
-      default: '',
-    },
-    emptyStateSvgPath: {
-      type: String,
-      required: true,
-    },
-  },
-  data() {
-    return {
-      showForm: false,
-    };
-  },
-};
-</script>
-
-<template>
-  <div>
-    <on-demand-scans-form
-      :help-page-path="helpPagePath"
-      :project-path="projectPath"
-      :default-branch="defaultBranch"
-    />
-  </div>
-</template>

ee/spec/frontend/on_demand_scans/components/on_demand_scans_app_spec.js

-import { shallowMount } from '@vue/test-utils';
-import { merge } from 'lodash';
-import OnDemandScansApp from 'ee/on_demand_scans/components/on_demand_scans_app.vue';
-import OnDemandScansForm from 'ee/on_demand_scans/components/on_demand_scans_form.vue';
-import { TEST_HOST } from 'helpers/test_constants';
-
-const helpPagePath = `${TEST_HOST}/application_security/dast/index#on-demand-scans`;
-const projectPath = 'group/project';
-const defaultBranch = 'master';
-const emptyStateSvgPath = `${TEST_HOST}/assets/illustrations/alert-management-empty-state.svg`;
-const newSiteProfilePath = `${TEST_HOST}/${projectPath}/-/security/configuration/dast_scans`;
-
-describe('OnDemandScansApp', () => {
-  let wrapper;
-
-  const findOnDemandScansForm = () => wrapper.find(OnDemandScansForm);
-
-  const expectForm = () => {
-    expect(wrapper.find(OnDemandScansForm).exists()).toBe(true);
-  };
-
-  const createComponent = (options) => {
-    wrapper = shallowMount(
-      OnDemandScansApp,
-      merge(
-        {},
-        {
-          propsData: {
-            helpPagePath,
-            projectPath,
-            defaultBranch,
-            emptyStateSvgPath,
-            newSiteProfilePath,
-          },
-        },
-        options,
-      ),
-    );
-  };
-
-  beforeEach(() => {
-    createComponent();
-  });
-
-  afterEach(() => {
-    wrapper.destroy();
-    wrapper = null;
-  });
-
-  describe('form', () => {
-    it('renders the form', () => {
-      expectForm();
-    });
-
-    it('passes correct props to OnDemandScansForm', () => {
-      expect(findOnDemandScansForm().props()).toMatchObject({
-        helpPagePath,
-        projectPath,
-        defaultBranch,
-      });
-    });
-  });
-});