You can set this rule up under Admin > Workflows > Automations > Time triggers tab > New Rule.


Condition: 

In Tickets > If Hours since Ticket Overdue > Greater than > 0


Action: 

Delete the Ticket


Please make sure to turn OFF the rule once the Overdue Tickets are deleted.


Note: This automation rule will run every hour and only process tickets that have been updated in the last 30 days.