Some issues with the Hibernate example

[lukaseder]

I'm currently translating some of the Java/Hibernate examples to jOOQ and found a few issues that you may or may not want to address:

CustomerService::deleteCustomer fails when orders have OrderProduct entries:

This query here:

https://github.com/cockroachdb/examples-orms/blob/8aacfca23a8b91667aad846e7e41e4e14c7658cc/java/hibernate/src/main/java/com/cockroachlabs/services/CustomerService.java#L83

Will fail in case there are entries in order_products, which does not have ON DELETE CASCADE clauses on its foreign keys by default (I think). I'm not sure if this is desired here.

OrderService::deleteOrder fails because of wrong query:

This query here:

https://github.com/cockroachdb/examples-orms/blob/8aacfca23a8b91667aad846e7e41e4e14c7658cc/java/hibernate/src/main/java/com/cockroachlabs/services/OrderService.java#L83

Will fail because the Order entity doesn't have an order_id column. I think the intention here was to delete the record in order_products