supermacservice
There are many places you'll need to update if you want to fully remove it as it's a required field. However, you can make it hidden and have a default selected all the time. That way you don't see it but you don't have to modify many places in the code to remove the requirement. Here is a start include/staff/ticket-open.inc.php. You are always on your own with any customizations! Good luck!
Cheers.
