nixos/no-x-libs: Switch to using nixpkgs.overlays
nixos/no-x-libs: Switch to using nixpkgs.overlays

The usage of nixpkgs.config.packageOverrides is deprecated and we do
have overlays since quite a while.

Signed-off-by: aszlig <ee1aa092358634f9c53f01b5a783726c9e21b35a@nix.build>
Cc: da39a3ee5e6b4b0d3255bfef95601890afd80709@edolstra

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