<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def forget(empowered, powerupClass, interface):
 """ Forgets powerups previously stored with ``remember``. :param empowered: The Empowered (Store or Item) to be powered down. :type empowered: ``axiom.item.Empowered`` :param powerupClass: The class for which powerups will be forgotten. :type powerupClass: class :param interface: The interface the powerups were installed for. :type interface: ``zope.interface.Interface`` :returns: ``None`` :raises ValueError: Class wasn't previously remembered. """

    className = fullyQualifiedName(powerupClass)
    withThisName = _StoredByName.className == className
    items = empowered.store.query(_StoredByName, withThisName)

    if items.count() == 0:
        template = "No named powerups for {} (interface: {})".format
        raise ValueError(template(powerupClass, interface))

    for stored in items:
        empowered.powerDown(stored, interface)
        stored.deleteFromStore()