nixosConfigurations: identifiers are specified redundantly

[steveej]

this makes room for mistakes.

example of linux-builder-01 (just looking at the definitions, not usage examples)

modules/flake-parts/nixosConfigurations.linux-builder-01/default.nix
7:  flake.nixosConfigurations.linux-builder-01 = inputs.nixpkgs.lib.nixosSystem rec {

modules/flake-parts/nixosConfigurations.linux-builder-01/configuration.nix
24:  networking.hostName = "linux-builder-01"; # Define your hostname.

[steveej]

i changed the labels on this because it's not technically a bug itself. however it does often lead to short-term bugs for me when developing.