polyfill: don't ship unused mtools package

hosts/common/polyunfill.nix

@@ -71,6 +71,13 @@ in
     }) filtered;
   };
 
+  options.system.fsPackages = lib.mkOption {
+    # <repo:nixos/nixpkgs:nixos/modules/tasks/filesystems/vfat.nix>  adds `mtools` and `dosfstools`
+    # dosfstools actually makes its way into the initrd (`fsck.vfat`).
+    # mtools is like "MS-DOS for Linux", ancient functionality i'll never use.
+    apply = lib.filter (p: p != pkgs.mtools);
+  };
+
   config = {
     # disable non-required packages like nano, perl, rsync, strace
     environment.defaultPackages = [];