Remove admin_user helper method from SystemHelpers module (#34096)

spec/system/admin/settings/appearance_spec.rb

@@ -3,9 +3,14 @@
 require 'rails_helper'
 
 RSpec.describe 'Admin::Settings::Appearance' do
+  let(:admin_user) { Fabricate(:admin_user) }
+
+  before { sign_in(admin_user) }
+
   it 'Saves changes to appearance settings' do
-    sign_in admin_user
     visit admin_settings_appearance_path
+    expect(page)
+      .to have_title(I18n.t('admin.settings.appearance.title'))
 
     fill_in custom_css_field,
             with: 'html { display: inline; }'