You no longer need to use create_function you can instead just use an anonymous function:
add_action( 'gform_preview_footer', create_function( '', 'GFFormDisplay::footer_init_scripts(' . $form['id'] . ');' ) );
Should be:
add_action( 'gform_preview_footer', function() use ($form){
GFFormDisplay::footer_init_scripts($form['id']);
});