Revert "nix/nixos-module/defaults: use non-nft iptables-legacy for migration"

This reverts commit 48b050b283.

nix/nixos-module/defaults.nix

@@ -54,11 +54,6 @@
     };
   };
 
-  nixpkgs.config.packageOverrides = pkgs: {
-    # TODO: remove when host is rebooted with a nixos-21.11 kernel
-    iptables = pkgs.iptables-legacy;
-  };
-
   documentation = {
     enable = false;
     nixos.enable = false;