common-updater-scripts: simplify fetchgit fix
common-updater-scripts: simplify fetchgit fix

No need to try evaluate the URL twice as introduced in the original fix
https://github.com/NixOS/nixpkgs/commit/cce486838b6c52dedfec1c93f60ebadb72c48431

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs