Revert "use linuxkit (eventually)"

This reverts commit 8b6c630.

machines/sequoia/default.nix

@@ -29,18 +29,24 @@
   nix.buildCores = 20;
   users.nix.configureBuildUsers = true;
 
-  # note: needs github.com/nix-community/linuxkit-nix installed before this will work
+  # use nixbuild.net for distributed builds
   nix.distributedBuilds = true;
   nix.buildMachines = [{
-    hostName = "ssh://nix-linuxkit";
+    hostName = "eu.nixbuild.net";
     system = "x86_64-linux";
-    sshKey = "/Users/brianhicks/.cache/nix-linuxkit-builder/keys/client";
-    maxJobs = 20;
-    supportedFeatures = [ "benchmark" "big-parallel" "kvm" ];
+    maxJobs = 100;
+    supportedFeatures = [ "benchmark" "big-parallel" ];
   }];
   nix.extraOptions = ''
     builders-use-substitutes = true
   '';
+  programs.ssh.knownHosts = {
+    nixBuild = {
+      hostNames = [ "eu.nixbuild.net" ];
+      publicKey =
+        "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPIQCZc54poJ8vqawd8TraNryQeJnvH1eLpIDgbiqymM";
+    };
+  };
 
   # dotfiles
   home-manager = {