Remove frontend usage and fix feature spec

Remove DOMContentLoaded since no longer recommended

ee/app/assets/javascripts/pages/projects/integrations/jira/issues/index.js

 import initJiraIssuesList from 'ee/integrations/jira/issues_list/jira_issues_list_bundle';
-import initIssuablesList from '~/issues_list';
 
-document.addEventListener('DOMContentLoaded', () => {
-  if (gon.features.jiraIssuesList) {
-    initJiraIssuesList({
-      mountPointSelector: '#js-jira-issues-list',
-    });
-  } else {
-    initIssuablesList();
-  }
-});
+initJiraIssuesList({ mountPointSelector: '#js-jira-issues-list' });

ee/spec/features/integrations/jira/jira_issues_list_spec.rb

@@ -11,6 +11,7 @@ RSpec.describe 'Jira issues list' do
     stub_licensed_features(jira_issues_integration: true)
     project.add_user(user, :developer)
     sign_in(user)
+    stub_request(:get, /.*jira.example.com.*/)
   end
 
   context 'when jira_issues_integration licensed feature is not available' do
@@ -26,7 +27,7 @@ RSpec.describe 'Jira issues list' do
     end
   end
 
-  it 'renders "Create new issue" button' do
+  it 'renders "Create new issue" button', :js do
     visit project_integrations_jira_issues_path(project)
 
     expect(page).to have_link('Create new issue in Jira')