Revert "Stub out the send letters page"

Reverts alphagov/notifications-admin#201

app/templates/main_nav.html

@@ -12,7 +12,6 @@
   <ul>
     <li><a href="{{ url_for('.choose_template', service_id=service_id, template_type='sms') }}">Text message templates</a></li>
     <li><a href="{{ url_for('.choose_template', service_id=service_id, template_type='email') }}">Email templates</a></li>
-    <li><a href="{{ url_for('.letters_stub', service_id=service_id) }}">Letter templates</a></li>
   </ul>
   {% endif %}
   {% if current_user.has_permissions(['manage_users', 'manage_settings']) %}

app/templates/views/letters.html

@@ -1,21 +0,0 @@
-{% extends "withnav_template.html" %}
-
-{% block page_title %}
-  Send letters – GOV.UK Notify
-{% endblock %}
-
-{% block maincolumn_content %}
-
-  <h1 class="heading-large">
-    {% if current_user.has_permissions(['send_letters']) %}
-      Send letters
-    {% else %}
-      Letter templates
-    {% endif %}
-  </h1>
-
-  <p>
-    This page is where you would go to send letters.
-  </p>
-
-{% endblock %}