Interfaces can be deleted by simply selecting the realm node where the interface you want to delete is running, and select the 'Interfaces' tab. From the table of configured interfaces, you can simply select the interface you want to delete and click the 'Delete Interface' button.
This will prompt you with a question to confirm the deletion of the selected interface. Clicking yes will stop the interface, closing all clients connected to the interface, then it will remove the interface from the realm. The image below shows the confirm dialog.