Remove link to integration testing page

This page has ben deprecated.

app/templates/views/documentation.html

@@ -23,7 +23,6 @@
       <li><a href="https://docs.notifications.service.gov.uk/{{ key }}.html" target="_blank" rel="noopener">{{ label }}</a></li>
     {% endfor %}
   </ul>
-  <p>You can also find out about <a href="{{ url_for('main.integration_testing')}}">integration testing</a> and the different types of API keys that you can use.</p>
   </div>
 </div>