In the Ohanah 3 we opted for not allowing delete on orders and attendees. This is by design to avoid problems with some scenarios. Because of that, we introduced "void" status so you know that order/ticket is invalid, but still have it for historical purposes.
On the other hand, during the testing phase there can be "junk" in there. Unfortunately, at this moment, the only way to delete those is via a database. You just need to truncate the following database tables:
You can use your usual DB tool, like phpmyadmin, for example, to do this job