nixos: rename.nix: fix bugs
nixos: rename.nix: fix bugs

Introduced in 286b007bd327a1e8d6d1fe66702b951f2fd6e29a and then
in 2e6b796761672e0e3ed685487007bb0d99126d91.

This a proper fix for what 70c6f6572dda0f2516bad812857ef814ec710a12 tried to do.
Removing the "config" prefix triggers the bug on pure nixos too, not only
on nixops.

NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs