nixos: zsh: Remove hack for zsh-nix-completions on nix 2.4

The zsh-nix-completions package now sets a priority, which helps avoid
conflicts with newer nix versions without patching the package from
the module.

nixos/modules/programs/zsh/zsh.nix

···
     # see https://github.com/NixOS/nixpkgs/issues/132732
     environment.etc.zinputrc.text = builtins.readFile ./zinputrc;
 
-    environment.systemPackages =
-      let
-        completions =
-          if lib.versionAtLeast (lib.getVersion config.nix.package) "2.4pre"
-          then
-            pkgs.nix-zsh-completions.overrideAttrs
-              (_: {
-                postInstall = ''
-                  rm $out/share/zsh/site-functions/_nix
-                '';
-              })
-          else pkgs.nix-zsh-completions;
-      in
-      [ pkgs.zsh ]
-      ++ optional cfg.enableCompletion completions;
+    environment.systemPackages = [ pkgs.zsh ]
+      ++ optional cfg.enableCompletion pkgs.nix-zsh-completions;
 
     environment.pathsToLink = optional cfg.enableCompletion "/share/zsh";