Render API callback: Moves entity_reference specific Form API elements (i.e. 'handler_settings') up a level for easier processing by the validation and submission handlers.
_entity_reference_field_settings_process()
function _entity_reference_form_process_merge_parent($element) {
$parents = $element['#parents'];
array_pop($parents);
$element['#parents'] = $parents;
return $element;
}