formatter: Remove mdsh from nix fmt configuration

Remove `mdsh` from the `nix fmt` configuration.
Making `nix fmt` and `nix flake check` take a little less resources,
since `mdsh` is currently not used.

Author: a-kenji

treefmt/flake-module.nix

@@ -5,7 +5,6 @@
   perSystem = { config, pkgs, ... }: {
     treefmt = {
       projectRootFile = "flake.nix";
-      programs.mdsh.enable = true;
       programs.nixpkgs-fmt.enable = true;
       programs.shellcheck.enable = true;
       programs.shfmt.enable = true;