In ActiveDEMAND, a list is just a view of contacts. Deleting a list will not delete the contacts.
Bulk deleting contacts can only be done via the 'All Contacts (Contacts->All Contacts) screen. This can be done by bulk selecting the contacts you want to delete, either by building a temporary contact segment in the all contacts segment builder, or by selecting an existing contact segment or an existing contact list.
Go to All contacts (Contacts->All Contacts)
Click the 'All Contacts' drop down to select your list or segment. Once the list or segment is selected and used to filter the all contacts table, click the checkbox on the top left column
Select Delete Contact from the dropdown, and click Submit