Don't use the header when we don't need it.

core/nginx/conf/proxy.conf

@@ -10,6 +10,7 @@ proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 proxy_set_header X-Forwarded-By $realip_remote_addr;
 {% else %}
 proxy_set_header X-Forwarded-For $remote_addr;
+proxy_hide_header X-Forwarded-By;
 {% endif %}
 proxy_http_version 1.1;
 proxy_hide_header Forwarded;