This code snippet will remove all sidebars (including header-right area), remove all layouts other than full-width, and force full-width to be selected by default in a Genesis child theme.

functions.php

//* Remove sidebars and header widget area
unregister_sidebar( 'header-right' );
unregister_sidebar( 'sidebar' );
unregister_sidebar( 'sidebar-alt' );

//* Unregister layout settings
genesis_unregister_layout( 'content-sidebar' );
genesis_unregister_layout( 'sidebar-content' );
genesis_unregister_layout( 'content-sidebar-sidebar' );
genesis_unregister_layout( 'sidebar-content-sidebar' );
genesis_unregister_layout( 'sidebar-sidebar-content' );

//* Force full width layout selection
add_filter( 'genesis_pre_get_option_site_layout', 'genesis_do_layout' );
function genesis_do_layout( $opt ) {
    $opt = 'full-width-content';
    return $opt;
}