Remove unused divs around subtitle exactly like title

... this is where per-field template selection would be great... Fences module
i think it was.

agaric/templates/field/field--field-subtitle.html.twig

@@ -0,0 +1,53 @@
+{#
+/**
+ * @file
+ * Theme override for a field.
+ *
+ * To override output, copy the "field.html.twig" from the templates directory
+ * to your theme's directory and customize it, just like customizing other
+ * Drupal templates such as page.html.twig or node.html.twig.
+ *
+ * Instead of overriding the theming for all fields, you can also just override
+ * theming for a subset of fields using
+ * @link themeable Theme hook suggestions. @endlink For example,
+ * here are some theme hook suggestions that can be used for a field_foo field
+ * on an article node type:
+ * - field--node--field-foo--article.html.twig
+ * - field--node--field-foo.html.twig
+ * - field--node--article.html.twig
+ * - field--field-foo.html.twig
+ * - field--text-with-summary.html.twig
+ * - field.html.twig
+ *
+ * Available variables:
+ * - attributes: HTML attributes for the containing element.
+ * - label_hidden: Whether to show the field label or not.
+ * - title_attributes: HTML attributes for the title.
+ * - label: The label for the field.
+ * - multiple: TRUE if a field can contain multiple items.
+ * - items: List of all the field items. Each item contains:
+ *   - attributes: List of HTML attributes for each item.
+ *   - content: The field item's content.
+ * - entity_type: The entity type to which the field belongs.
+ * - field_name: The name of the field.
+ * - field_type: The type of the field.
+ * - label_display: The display settings for the label.
+ *
+ * @see template_preprocess_field()
+ */
+#}
+{#
+  Ensures that the visually hidden option for field labels works correctly.
+  @todo: Remove when https://www.drupal.org/node/2779919 is resolved.
+#}
+{# Child templates can specify classes to be added to items. #}
+{% set item_classes = item_classes ?? ['subtitle'] %}
+
+{% for item in items %}
+  {%
+    set item = item|merge({
+      'attributes': item.attributes.addClass(item_classes)
+    })
+  %}
+  <h2{{ item.attributes }}>{{ item.content}} </h2>
+{% endfor %}