Remove the option to check for updates from Sandstorm installations.

resources/views/admin/index.twig

@@ -14,7 +14,9 @@
                     <ul>
                         <li><a href="{{ route('admin.configuration.index') }}">{{ 'firefly_instance_configuration'|_ }}</a></li>
                         <li><a href="{{ route('admin.links.index') }}">{{ 'journal_link_configuration'|_ }}</a></li>
+                        {% if not sandstorm %}
                         <li><a href="{{ route('admin.update-check') }}">{{ 'update_check_title'|_ }}</a></li>
+                        {% endif %}
                     </ul>
                 </div>
             </div>