Add Design System class to remove visited state from links

Co-Authored-By: Tom Byers <tombaromba@gmail.com>

app/templates/components/service-link.html

@@ -1,6 +1,6 @@
 {% macro service_link(service, endpoint, link_text) %}
   {% if service %}
-    <a class="govuk-link" href="{{ url_for(endpoint, service_id=service.id) }}">{{ link_text }}</a>
+    <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for(endpoint, service_id=service.id) }}">{{ link_text }}</a>
   {% else %}
     <b class="govuk-!-font-weight-bold">{{ link_text|capitalize }}</b>
   {% endif %}