Removed legacy advise to change HTTP_HOST

Nginx-Configuration.asciidoc

@@ -55,7 +55,6 @@ server {
 . `service php7.0-fpm start` #start php7.0-fpm daemon
 . `service nginx start` #start nginx webserver
 . If you want to use your custom domain to access admin page (e.g.: `http://mydomain.internal/admin/settings.php` instead of `http://pi.hole/admin/settings.php`), make sure `mydomain.internal` is assigned to `server_name` in `/etc/nginx/sites-available/default`. E.g.: `server_name mydomain.internal;`
-. To retain the functionality of the block page when directly accessing blacklisted domains, `$serverName = escapeshellcmd($_SERVER['SERVER_NAME']);` should be replaced with `$serverName = escapeshellcmd($_SERVER['HTTP_HOST']);` in `pihole/index.php`. With Nginx, if `server_name` is not defined in the server config it defaults to `""`, whereas in Lighttpd it defaults to `hostname`. (HTTP_HOST is already used in current version of pi-hole)
 . If you want to use block page for any blocked domain subpage (aka Nginx 404), add this to Pihole server block in your Nginx configuration file:
 ```
 error_page 404 /pihole/index.php