Use only the 2021 route in nginx

The old `/https-everywhere/` route now 404s on the securedrop.org
website, so we'll only honor the 2021 route. We should have implemented
a version scheme from day one. =)

docker/nginx.conf

@@ -22,9 +22,7 @@ http {
         location / {
             root /opt/nginx/root;
             index index.html;
-            # This line has been adjusted for the temporary different external URL.
-            # Don't include this change in the main branch.
-            rewrite ^/https-everywhere($|//+)(.*) /https-everywhere-2021/$2 permanent;
+            rewrite ^/https-everywhere-2021($|//+)(.*) /https-everywhere-2021/$2 permanent;
         }
     }
 }