Hi @aldoreyes
This is a bit of a tricky one, but is possible with some logic as such:
1. Search the wp_postmeta table for any rows which have a value of $post_id
2. Delete these rows!
The database query will have to be a custom FIND sql statement, but this is easy to create thanks to the wpdb functions. You can read more about this here:
http://codex.wordpress.org/Class_Reference/wpdb