Prepares 'extra fields' for the current run-time context.
The functionality has moved to the FieldInfo class. This function is kept as a backwards-compatibility layer. See http://drupal.org/node/1915646.
FieldInfo::prepareExtraFields()
function _field_info_prepare_extra_fields($extra_fields, $entity_type, $bundle) {
$cache = _field_info_field_cache();
return $cache
->prepareExtraFields($extra_fields, $entity_type, $bundle);
}