Remove all Contentful-related code from the project

* Drops the contentful app: views, models and templates
* Drops Contentful-related settings
* Drop static bundles that appeared to be for Contentful components only
* Updates DB export script to not dump the contentful table
* Does NOT do anything to automatically drop the contentful_ DB tables, however
* Remove use of prefer_cms decorator for VPN RC views and moves the routing to cms_only_urls so that we can still reverse those page addresses
* Move legacy /more/ redirects related to the VPN pages to global redirects (losing the locale-availability check, but deferring it to the CMS to 404 or not instead)

Author: stevejalim

bedrock/base/templates/cron-health-check.html

@@ -89,16 +89,6 @@ <h1 id="other-data">Other Site Data</h1>
         <td>{{ most_recent_data_change_ts }}</td>
       </tr>
       {% endif %}
-      <tr>
-        <td><b>Latest Contentful sync</b></td>
-        <td{% if contentful_info.latest_sync %} title="{{contentful_info.latest_sync|datetime(settings.STRFTIME_FORMAT_INTERNAL_USE)}}"{% endif %}>
-          {% if contentful_info.time_since_latest_sync %}
-            {{ contentful_info.time_since_latest_sync }}
-          {% else %}
-            No data!
-          {% endif %}
-        </td>
-      </tr>
     </tbody>
   </table>