They are automatically removed on periodic updates, about every two hours.
If I remember, you can also use a trick to remove/hide items.....
Go to the Store tab and on lower left click the link for "Store Items". Locate the item in the table, select/check the box to left of item, and use the make hidden button. I believe that both hides the item from appearing in the Auctiva Store and the SG.
Danno