Use the below Custom PHP Code to hide featured image on.
You can add the below snippets to your functions.php file or you can use the Code Snippet plugin to add the same.
Custom PHP Code
add_action( 'after_setup_theme','gp_remove_featured_page_header' );
if (!function_exists('gp_remove_featured_page_header')) {
function gp_remove_featured_page_header() {
remove_action( 'generate_before_content', 'generate_featured_page_header_inside_single', 10 );
}
}