To remove a contact from all lists, you need to start with the contact's detail data and simply remove all of the <ContactList> elements from the <ContactLists> element, and issue the PUT method on the contact resource:
https://api.constantcontact.com/ws/customers/{username}/contacts/{contact-id}
Removing a contact does not mean that the contact has unsubscribed or
opted out of receiving emails. It means the contact simply does not
belong to any particular contact list, and can be added back to a list
by the account owner. However, this API should not be used if the
contact has unsubscribed from receiving all emails. Instead, you must opt-out the contact.
