If you no longer want to sell the item, click the right [...] button → "Deactivate"
Deactivating the item will hide it from the app, and users will not able to purchase the item.
However, users who have already pruchased the item before deactivation will be able to continue using the item.
Please note that 24 hours must pass since the point of deactivation in order to reactivate a deactivated item!