Don't include tab-content--comments-enabled in initial response

Let the JS add this when it's ready

wagtail/admin/templates/wagtailadmin/edit_handlers/tabbed_interface.html

@@ -30,7 +30,7 @@
     {% endif %}
 </div>
 
-<div class="tab-content tab-content--comments-enabled">
+<div class="tab-content">
     {% for child in self.children %}
         <section id="tab-{{ child.heading|cautious_slugify }}" class="{{ child.classes|join:" " }} {% if forloop.first %}active{% endif %}" role="tabpanel" aria-labelledby="tab-label-{{ child.heading|cautious_slugify }}" data-tab="{{ child.heading|cautious_slugify }}">
             {{ child.render_as_object }}

wagtail/admin/tests/test_edit_handlers.py

@@ -315,7 +315,7 @@ class TestTabbedInterface(TestCase):
         self.assertIn('<a href="#tab-speakers" class="" data-tab="speakers">Speakers</a>', result)
 
         # result should contain tab panels
-        self.assertIn('<div class="tab-content tab-content--comments-enabled">', result)
+        self.assertIn('<div class="tab-content">', result)
         self.assertIn('<section id="tab-event-details" class="shiny active" role="tabpanel" aria-labelledby="tab-label-event-details" data-tab="event-details">', result)
         self.assertIn('<section id="tab-speakers" class=" " role="tabpanel" aria-labelledby="tab-label-speakers" data-tab="speakers">', result)