If you want to remove the entire twentytwelve_scripts_styles function, you have to remove the action hook :
remove_action( 'wp_enqueue_scripts', 'twentytwelve_scripts_styles' );
However, this code have to execute after the function is being hooked by Twenty Twelve code, and before the action is fired (because after it’s too late). The child theme functions.php file is loaded before the Twenty Twelve one, so you have to call remove_action from an action that fires before wp_enqueue_scripts, for example init.
add_action( 'init', 'answer_215713_override_twentytwelve_script' );
function answer_215713_override_twentytwelve_script(){
remove_action( 'wp_enqueue_scripts', 'twentytwelve_scripts_styles' );
}
The tutorial that you linked says :
[…] you need to attach this function to a hook which will fire after the hook which the parent theme function is attached to. This is because you can’t remove the action before it’s been fired.
I think this is wrong. The opposite is true : you have to attach your function to a hook that will fires before the hook it was attached by the parent theme, or else it will be to late to cancel the action. In fact, you can’t remove actions after they have been fired (it’s useless).