Revert "ncdns: pin to go 1.16"

This reverts commit cee6ccfc754af33f9fb03b15b938707c584a6342.

pkgs/top-level/all-packages.nix

···
 
   unit = callPackage ../servers/http/unit { };
 
-  ncdns = callPackage ../servers/dns/ncdns {
-    buildGoModule = buildGo116Module;
-  };
+  ncdns = callPackage ../servers/dns/ncdns { };
 
   nginx = nginxStable;