profiles/graphical.nix: Drop systemWide pulseaudio in iso

[etu]

Motivation for this change

It's not needed since #66338 and should have been done earlier.

This is based on a follow-up on #56167.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @

[worldofpeace]

Did the users of graphical.nix ever use a root user?
It appears Demo user account is what's used in demo.nix, so I'm not sure this was ever needed.

[worldofpeace]

LGTM, no testing done but I believe it was unneeded anyway. We could probably backport it even.

[etu]

@worldofpeace

Did the users of graphical.nix ever use a root user?

Yes it did. That's why I added that line. I tested it myself both before and after adding the line on actual hardware.

It appears Demo user account is what's used in demo.nix, so I'm not sure this was ever needed.

I'm not sure what demo.nix is for...

[worldofpeace]

@etu I believe it's for the ova. We have this annoying inconsistency with the ISO's and the OVA.
Even worse is we've documented and exposed them https://nixos.org/nixos/manual/index.html#sec-profile-demo, https://nixos.org/nixos/manual/index.html#sec-profile-graphical. I really hope no one was using this.

[worldofpeace]

#66338 is in 19.09 so I think we should backport this.

[etu]

@worldofpeace Yeah, we should. I'll look into it later today unless someone does it before me.