shell: partially revert "add nh over nixos-rebuild alias"

This reverts commit a984633ee3.

I actually prefer lix's multiline-with-logs output over nom,
so nh is not much better to use over nixos-rebuild-ng

I am still keeping around nh though, for eg `nh search`

defaults/shell.nix

@@ -52,6 +52,8 @@ in
     environment.shellAliases = {
       # make nix-shell preserve the user's $SHELL
       nix-shell = /* sh */ ''nix-shell --command "export SHELL=$SHELL; $SHELL"'';
+
+      nixos-rebuild = /* sh */ "nixos-rebuild --ask-sudo-password";
     };
 
     environment.systemPackages = lib.mkIf config.nixowos.allowAddingPackages cfg.extraPackages;