remove build dependency

default.nix

@@ -1,9 +1,4 @@
-{ pkgs ? import <nixpkgs> {
-    overlays = [
-      (import (fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz"))
-    ];
-  }
-}:
+{ pkgs ? import <nixpkgs> { } }:
 with pkgs;
 let
   agent = callPackage "${fetchgit {
@@ -18,10 +13,7 @@ rustPlatform.buildRustPackage
   name = "wireguard-agent";
   src = nix-gitignore.gitignoreSource [ ] ./.;
 
-  nativeBuildInputs = [ 
-    (rust-bin.fromRustupToolchainFile ./rust-toolchain.toml)    
-    agent
-  ];
+  nativeBuildInputs = [ agent ];
 
   cargoLock = {
     lockFile = ./Cargo.lock;
@@ -33,6 +25,8 @@ rustPlatform.buildRustPackage
 
   doCheck = false;
 
+  RUSTC_BOOTSTRAP = true;
+
   AGENT_PATH = "${agent}/bin/agent_harness";
   KEY_FILE = "keyfile";
   RUST_LOG = "debug";