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/verification-not-received.html

@@ -1,4 +1,5 @@
 {% extends "withoutnav_template.html" %}
+{% from "components/button/macro.njk" import govukButton %}
 
 {% block per_page_title %}
   Resend verification code
@@ -16,7 +17,11 @@
 
 
       <p>
-      <a class="button" href="{{url_for('main.check_and_resend_verification_code')}}" role="button">Resend security code</a>
+        {{ govukButton({
+          "element": "a",
+          "text": "Resend security code",
+          "href": url_for('main.check_and_resend_verification_code')
+        }) }}
       </p>
   </div>
 </div>