Add default.nix file updates

I didn't check that I added every change, oops.

default.nix

@@ -1,15 +1,2 @@
-with import <nixpkgs> { };
-let
-  t = terraform.withPlugins (p: [
-    p.libvirt
-    p.local
-    p.null
-    p.random
-    p.shell
-    p.template
-    p.tls
-  ]);
-in
-mkShell {
-  buildInputs = [ gnumake ];
-}
+with import <nixpkgs> {};
+mkShell { buildInputs = [ gnumake ]; }