nixos/rename: drop system.nixos.{stateVersion, defaultChannel}

[worldofpeace]

Comment said to remove these before 18.09 was released :(

Motivation for this change

I'm not sure if the comment in the file isn't valid anymore?
But I'm guessing we should remove these now.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option 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 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)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[samueldr]

cc @lheckemann RM for 19.09, just in case, but it's probably fine to remove.

From memory it was because for a short while between 18.03 and 18.09, unstable users could have built a system with a now reverted change for the option name. For reference, it starts with good intentions in #39447

[worldofpeace]

From memory it was because for a short while between 18.03 and 18.09, unstable users could have built a system with a now reverted change for the option name. For reference, it starts with good intentions in #39447

Yep, I recall that. Shouldn't be a problem for us to drop this in 19.03 also.

[worldofpeace]

Going for it