Motivation for this change

This is necessary to support such use as:

{
  config = {
    environment.etc = {
      "resolv.conf".text = "nameserver 127.0.0.1\n";
    };
}

When /nix/store is read-only this already works except that resolvconf warns that it can not update /etc/resolv.conf; when /nix/store is writable, without this change resolvconf corrupts the store.

When config.services.resolved.enable = true, config.environment.etc."resolv.conf" is defined, so keeping the old conditional is redundant:

Things done

I have tested this PR with all combination of settings: services.resolved.enable = true | false, environment.etc = { "resolv.conf" = } | { }, services.dnsmasq.enable = true | false. It does not break anything and works as intended.

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.