Preventing header resizing in twenty-eleven theme

I am building a child theme for twenty-eleven. I came across this closed thread referring to commenting out 2 lines in the functions.php in the parent theme folder.
https://www.ads-software.com/support/topic/how-to-prevent-resizing-of-custom-header-image-twenty-ten?replies=6

Is there a way to override this. It seems he refers to a way but there isn’t really any conclusion in that thread it seems whether or not that works. Here is the part of the thread I am interested in looking into a bit more. Ideally, of course, I would prefer to make the modifications in the child themes functions.php file, not the parent.

The following lines are quoted from that thread.

There is also a function remove_theme_support(), not sure if it works in reverse, try adding nested inside you child themes after_setup_theme function.

/* Remove theme support for Post Thumbnails */
function remove_custom_theme_support(){
	remove_theme_support('post-thumbnails');
}
add_action( 'after_setup_theme', 'remove_custom_theme_support', 11 );