Fix error due to glitch-soc's theming system

app/views/admin/instances/index.html.haml

@@ -1,9 +1,6 @@
 - content_for :page_title do
   = t('admin.instances.title')
 
-- content_for :header_tags do
-  = javascript_pack_tag 'admin', async: true, crossorigin: 'anonymous'
-
 - content_for :heading_actions do
   - if whitelist_mode?
     = link_to t('admin.domain_allows.add_new'), new_admin_domain_allow_path, class: 'button', id: 'add-instance-button'