home-manager/common: Use new upstream nix.settings to configure Nix

home-manager/configs/castle.nix

@@ -15,7 +15,6 @@
             hostname = "h.nul.ie";
             sshOpts = [ "-4" "-p" "8022" ];
           };
-          nix.config.cores = "16";
         };
 
         home.packages = with pkgs; [
@@ -23,6 +22,8 @@
           mame
         ];
 
+        nix.settings.cores = 16;
+
         programs = {
           ssh.matchBlocks = {
             home = {

home-manager/configs/macsimum.nix

@@ -9,9 +9,10 @@
       {
         my = {
           deploy.enable = false;
-          nix.config.cores = "6";
         };
 
+        nix.settings.cores = 6;
+
         programs = {
           ssh.enable = false;
         };