add_action not using ‘delete_post’ action with wp_delete_post

You need to use before_delete_post action. As its already very late when delete_post action is run. WordPress un-attach all the attachments before running delete_post action. So when you run get_posts in your delete_attachment function there are no attachments found.

So you need to hook your function to before_delete_post.

add_action('before_delete_post','abc_delete_attachment');