irods: Don't use builtins.nixVersion
irods: Don't use builtins.nixVersion

The value of builtins.nixVersion should never be used except to bail
out if it's too old. It causes the evaluation result to depend on the
version of Nix, so e.g. the binary cache doesn't work.

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