Callback triggered for entity before deleted.

~~~
<?php
function my_component_init(){
ossn_register_callback('entity', 'before:delete',, 'my_component_cb');
}
function my_component_cb($callback, $type, $params){
//$params['guid'] contains entity guid going to be deleted.
}
ossn_register_callback('ossn', 'init', 'my_component_init');
~~~

Note that the entity won't exists after deletation so you can use `ossn_get_entity` before deltation but not after.