Remove unnecesary mention of self from flake.nix

flake.nix

@@ -3,7 +3,7 @@
   inputs.self.submodules = true;
 
   outputs =
-    { self, nixpkgs, ... }:
+    { nixpkgs, ... }:
     let
       system = "x86_64-linux";
       pkgs = nixpkgs.legacyPackages.${system};
@@ -13,7 +13,7 @@
         version = "0.0.1";
 
         src = pkgs.lib.cleanSourceWith {
-          src = "${self}/libs";
+          src = ./libs;
           name = "mruby-src";
         };
 
@@ -39,7 +39,7 @@
         pname = "kutu";
         version = "0.1.0";
 
-        src = self;
+        src = ./.;
 
         nativeBuildInputs = with pkgs; [
           dune_3