Remove deprecated 'X-XSS-Protection' header (#6871)

data/conf/nginx/templates/sites-default.conf.j2

@@ -14,7 +14,6 @@ ssl_session_tickets off;
 
 add_header Strict-Transport-Security "max-age=15768000;";
 add_header X-Content-Type-Options nosniff;
-add_header X-XSS-Protection "1; mode=block";
 add_header X-Robots-Tag none;
 add_header X-Download-Options noopen;
 add_header X-Frame-Options "SAMEORIGIN" always;