Remove guidance on external link icons

We no longer style differently them in toolkit.

app/views/guide_typography.html

@@ -131,29 +131,6 @@ <h3 class="heading-medium" id="typography-links">Links</h3>
 <code class="language-markup">
   {% include "snippets/encoded/typography_links.html" %}
 </code>
-</pre>
-
-  <h4 class="heading-medium" id="typography-external-links">External links</h4>
-
-  <div class="panel panel-border-wide text">
-    <p>
-      <strong class="bold-small">External link styles are deprecated and are liable to be removed in a future release.</strong>
-    </p>
-    <p>
-      If your service has user research that indicates that external links are useful (or not) then we’d like to hear from you either on Slack, <a href="https://groups.google.com/a/digital.cabinet-office.gov.uk/forum/#!forum/digital-service-designers">digital-service-designers</a> or <a href="https://github.com/alphagov/govuk_elements/issues/new">opening an issue</a>.
-    </p>
-  </div>
-
-  <div class="example">
-    <div class="text">
-      {% include "snippets/typography_external_links.html" %}
-    </div>
-  </div>
-
-<pre>
-<code class="language-markup">
-  {% include "snippets/encoded/typography_external_links.html" %}
-</code>
 </pre>
 
   <h3 class="heading-medium" id="typography-lists">Lists</h3>