nixos/firefox-syncserver: remove extra add_header

syncstorage-rs sets this header starting with 0.12.3.

nixos/modules/services/networking/firefox-syncserver.nix

@@ -313,10 +313,6 @@ in
         forceSSL = cfg.singleNode.enableTLS;
         locations."/" = {
           proxyPass = "http://127.0.0.1:${toString cfg.settings.port}";
-          # source mentions that this header should be set
-          extraConfig = ''
-            add_header X-Content-Type-Options nosniff;
-          '';
         };
       };
     };