Test letter too long error banner using exisitng data-error-type attribute

This way we can avoid both creating an id attribute for testing
and testing by content.

app/templates/views/check/ok.html

@@ -26,7 +26,7 @@
   ) }}
 
   {% if letter_too_long %}
-    {% call banner_wrapper(type='dangerous', id='letter-too-long') %}
+    {% call banner_wrapper(type='dangerous') %}
         {% include "partials/check/letter-too-long.html" %}
     {% endcall %}
   {% endif %}