Remove flake-utils dependency

flake.nix

@@ -1,14 +1,25 @@
 {
-  description = "";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable-small";
 
-  inputs.flake-utils.url = "github:numtide/flake-utils";
+  outputs =
+    { self, nixpkgs, ... }:
+    let
+      system = "x86_64-linux";
+    in
+    {
+      devShells."${system}".default =
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+          };
+        in
+        pkgs.mkShell {
+          packages = with pkgs; [
+            clang
+            platformio
+          ];
 
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem
-      (system:
-        let pkgs = nixpkgs.legacyPackages.${system}; in
-        {
-          devShell = import ./shell.nix { inherit pkgs; };
-        }
-      );
+          shellHook = "";
+        };
+    };
 }