Since you are using Genesis, why don’t you just use the Layout that doesn’t contain Primary Sidebar? The layout option should be available right below the editor (as a meta box).
If you still need code, use plain CSS to remove the sidebar area.
function remove_primary_sidebar() {
//Only if Pages with the following IDs
if (is_page(array('1', '2', '3'))) { ?>
<style type="text/css">
.sidebar-primary {display:none !important;}
</style>
<?php }
}
add_action('wp_head', 'remove_primary_sidebar');