remove image sizes in child-theme

Hi,
I have made a child theme for a theme that generates several additional image sizes in its functions.php
here is the code:

if ( function_exists( 'add_theme_support' ) ) {
	add_theme_support( 'post-thumbnails' );
	set_post_thumbnail_size( 125, 125, true ); // Normal post thumbnails
	add_image_size( 'wide-feature', 900, 300, true ); // Wide feature images
	add_image_size( 'medium-feature', 450, 300, true ); // Medium feature images
	add_image_size( 'single-image', 590, 300, true ); // Single / Portfolio image
	add_image_size( 'portfolio-thumbnail', 280, 125, true ); // Portfolio thumbnails
	add_image_size( 'twocol-image', 435, 9999, true ); // Two col image
}

I want to remove these additional sizes in my child theme. Where do I hook in to do that? Is there an remove_image_size tag?
Please help!