In order to delete a restriction please use the Query tool to select a restriction on the map. On the pop-up window showing details of the restriction please click the Delete button. You will be asked to confirm your action and when you do confirm that you indeed want to delete the restriction, the information about said restriction including its geometry will be wiped from the database.
Step 1: Query a restriction for deletion | Step 2: Confirm the intend to delete | Result: Restriction deleted |