remove build dependency

default.nix

@@ -1,18 +1,9 @@
-{ pkgs ? import <nixpkgs> {
-    overlays = [
-      (import (fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz"))
-    ];
-  }
-}:
+{ pkgs ? import <nixpkgs> { } }:
 with pkgs;
 rustPlatform.buildRustPackage
 {
   name = "wireguard-client";
   src = nix-gitignore.gitignoreSource [ ] ./.;
 
-  nativeBuildInputs = [ 
-    (rust-bin.fromRustupToolchainFile ./rust-toolchain.toml)    
-  ];
-
-  cargoSha256 = "sha256-3FnWeoFeD9/q16J0CpXL4/lIlP34jf1aUN6I8fBFZ0g=";
+  cargoLock.lockFile = ./Cargo.lock;
 }