Implements hook_field_info_alter().
function user_field_info_alter(&$info) {
// Add the 'user_register_form' instance setting to all field types.
foreach ($info as $field_type => &$field_type_info) {
$field_type_info += array(
'instance_settings' => array(),
);
$field_type_info['instance_settings'] += array(
'user_register_form' => FALSE,
);
}
}