Remove custom example plugin. (#25784)

docs/4.0/utilities/close-icon.md

@@ -8,8 +8,9 @@ toc: true
 
 **Be sure to include text for screen readers**, as we've done with `aria-label`.
 
-{% example html %}
+{% capture example %}
 <button type="button" class="close" aria-label="Close">
   <span aria-hidden="true">&times;</span>
 </button>
-{% endexample %}
+{% endcapture %}
+{% include example.html content=example %}