This sounds like is a really bad idea. Like selling a car without the car keys!

If you delete the wp-admin folder, the site will not work due to PHP errors.

You will also not be able to update such an install in a meaningful way.

Hand instead the theme or plugin to your client - don't modify or delete parts of the WordPress core.

This sounds like is a really bad idea. Like selling a car without the car keys!

If you delete the wp-admin folder, the site will not might not work due to PHP errors.

Many sites depend on ajax through /wp-admin/admin-ajax.php.

You will also not be able to update such an install in a meaningful way.

Hand instead the theme or plugin to your client - don't modify or delete parts of the WordPress core.