treewide: fix darwin, remove obsolete follow

flake.nix

@@ -116,7 +116,6 @@
     };
     crane = {
       url = "github:ipetkov/crane";
-      inputs.nixpkgs.follows = "nixpkgs";
     };
     firefox-darwin = {
       url = "github:bandithedoge/nixpkgs-firefox-darwin";

hosts/default.nix

@@ -66,9 +66,15 @@
 
       darwin =
         name: module:
-        baseDarwin._module.args.extendModules {
-          modules = [ module ];
-          specialArgs.configurationName = name;
+        let
+          eval = baseDarwin._module.args.extendModules {
+            modules = [ module ];
+            specialArgs.configurationName = name;
+          };
+        in
+        eval
+        // {
+          system = eval.config.system.build.toplevel;
         };
     };
 }