A Platform manager can follow the below steps to delete a list that they did not create.
  1. Any module
  2. Analysis > Manage lists
  3. Manage basic and advanced lists
  4. List admin
  5. Select the past user in the user drop-down
  6. Next to the list, you would like to remove click delete
  7. Click okay in the confirmation popup 
The delete button will be grayed out if it is being used for a distribution group.