Pull list of builders from actual config

Rather than maintaining a list of the hosts by name, we can pull that
from the list of hosts that are configured with my module.

hosts/default.nix

@@ -27,6 +27,7 @@ let
       inherit system;
       specialArgs = {
         inherit nixpkgs top overlays;
+        inherit (top) self;
       };
       modules = [
         {

modules/baseline.nix

@@ -2,10 +2,13 @@
   pkgs,
   config,
   lib,
+  self,
   ...
 }:
 let
-  builderHosts = [ "jude" "myself" ];
+  builderHosts = (
+    lib.attrNames (lib.filterAttrs (_: v: v.config.greg.remote-builder.enable) self.nixosConfigurations)
+  );
 in
 {
   # Enable flakes