Replace straightforward buttons and links styled like buttons

This replaces the buttons that aren't part of a macro and that we don't
need to write additional styles for with their govuk-frontend equivalent.

There were some links that were styled to look like buttons, so these
have also been replaced with the new govuk-frontend macro.

There was one button on the `choose-account.html` template that was in a
section of code that was never reached - this has been deleted.

app/templates/views/choose-account.html

@@ -1,4 +1,5 @@
 {% extends "withoutnav_template.html" %}
+{% from "components/button/macro.njk" import govukButton %}
 
 {% macro service_list(
   heading,
@@ -39,11 +40,6 @@
   {% else %}
     </ul>
   {% endif %}
-  {% if show_add_service_button %}
-    <div class="js-stick-at-bottom-when-scrolling">
-      <a href="{{ url_for('.add_service') }}" class="button-secondary">Add a new service</a>
-    </div>
-  {% endif %}
   <div class="keyline-block"></div>
 {% endmacro %}
 
@@ -112,7 +108,12 @@
           </div>
           <div class="column-three-quarters">
       {% endif %}
-      <a href="{{ url_for('.add_service') }}" class="button-secondary">Add a new service</a>
+      {{ govukButton({
+        "element": "a",
+        "text": "Add a new service",
+        "href": url_for('.add_service'),
+        "classes": "govuk-button--secondary"
+      }) }}
       {% if current_user.has_access_to_live_and_trial_mode_services %}
           </div>
         </div>