Simplify shell.nix.

Author: jgm

shell.nix

@@ -1,18 +1,12 @@
-{nixpkgs ? import <nixpkgs> {} }:
-let
-  inherit (nixpkgs) pkgs;
-
-  nixPackages = [
-    pkgs.clangStdenv
-    pkgs.cmake
-    pkgs.gdb
-    pkgs.python3
-    pkgs.perl
-    pkgs.re2c
-    pkgs.curl
+with (import <nixpkgs> {});
+mkShell {
+  buildInputs = [
+    clangStdenv
+    cmake
+    gdb
+    python3
+    perl
+    re2c
+    curl
   ];
-in
-pkgs.stdenv.mkDerivation {
-  name = "env";
-  buildInputs = nixPackages;
 }