Revert "Update site-defaults.conf (#3778)" (#3779)

This reverts commit b8ec9ad53618235588b6cda3dbf00fcf5b1dc5a9.

data/conf/nginx/includes/site-defaults.conf

@@ -4,9 +4,8 @@
   override_charset on;
 
   ssl_protocols TLSv1.2 TLSv1.3;
-  ssl_prefer_server_ciphers on;
-  ssl_ciphers ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;
-  ssl_ecdh_curve X25519:secp384r1:secp256r1;
+  ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384;
+  ssl_prefer_server_ciphers off;
   ssl_session_cache shared:SSL:50m;
   ssl_session_timeout 1d;
   ssl_session_tickets off;