Improve sif -> thor dist build ssh config

machines/sif/configuration.nix

@@ -59,27 +59,24 @@
 	nix = {
 		distributedBuilds = true;
 		buildMachines = [{
-			hostName = "thor";
-			systems = [
-    			"x86_64-linux"
+
+            hostName = "thor";
+            sshUser  = "riley";
+            sshKey   = "/root/.ssh/id_ed25519";
+
+            systems = [
+                "x86_64-linux"
                 "aarch64-linux"
-			];
+            ];
+
             supportedFeatures = [
                 "nixos-test"
                 "benchmark"
                 "big-parallel"
                 "kvm"
             ];
+
 		}];
 	};
 
-	programs.ssh.extraConfig = ''
-        Host thor
-            HostName thor
-            Port 22
-            User riley
-            IdentitiesOnly yes
-            IdentityFile /root/.ssh/id_ed25519
-    '';
-
 }