Remove message preview from row error page

Two reasons to remove this:

1. It’s potentially confusing because you’ll see a preview of the first
   message, but the first row might not appear in the table shown on
   screen if it doesn’t have any errors.

2. If there are row-level errors in your file then they’re not related
   to the template – it’s a distraction.

app/templates/views/check/row-errors.html

@@ -97,7 +97,4 @@
     </p>
   {% endif %}
 
-  <h2 class="heading-medium">Preview of {{ template.name }}</h2>
-  {{ template|string }}
-
 {% endblock %}