Motivation for this change

minecraft-server, as its name implies, is a server, and therefore isn't run with a GUI. Therefore, we can use jre_headless and avoid installing GTK.

(Actually, that's not quite true: the minecraft server does have an optional GUI, which is little more than a window with stdin/stdout and some CPU/memory stats. However, our wrapper script turns off the GUI with nogui anyway, so I don't think it matters.)

Tested by running the NixOS minecraft-server service and successfully connecting to the game.

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 nixpkgs-review --run "nixpkgs-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.