Revert "nixos/nix-daemon.nix: assert distributedBuilds and buildMachines!=[]"
Revert "nixos/nix-daemon.nix: assert distributedBuilds and buildMachines!=[]"

This reverts commit 67b6e5639126ab6e8ec5d2b303aa9736a626b609.
This reverts commit 250885d0caed9ab910e801d7a3c21d6f83d4cdae.

Causes issues for some configs, see https://github.com/NixOS/nixpkgs/commit/67b6e5639126ab6e8ec5d2b303aa9736a626b609

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