Child theme code for removing background and header

I am creating a child theme for Twentytwelve as the parent.

I want to remove the Dashboard options to change the header and background.

I managed to come up with the following code, it doesn’t crash the site, and it accomplishes what I intended without breaking anything (that I have discovered so far) but I want to make sure I am writing the code properly.

What is the correct way to write the following?

<?php

function twentytwelvechild_remove_custom_appearance() {
remove_theme_support( 'custom-background' );
remove_theme_support( 'custom-header' );
}
add_action( 'after_setup_theme', 'twentytwelvechild_remove_custom_appearance', 11 );

?>

That is the entire contents of my child’s functions.php