Removing entire "Link To" drop down menu in 3.5?

I’m trying to remove the entire “Link to” drop-down menu in the “Upload Media” section, under “Attachment Display Settings”. I was able to do this in WP versions prior to 3.5 with the following function:

<?php function my_function_to_remove_url_buttons ( $form_fields ) {
  unset($form_fields['url']);
  return $form_fields;
}
add_filter('attachment_fields_to_edit','my_function_to_remove_url_buttons',10,1); ?>

This is no longer working in 3.5, however. Can anyone help me make this work in the new version? Help would be greatly appreciated!