This method is used to delete files stored as attachments or under S-Drive folders.
List<ResultObject> deleteFiles(List<ID> wipIds, String objectId)
Parameters:
wipIds: List of Salesforce.com IDs of "file" records (either attachments or S-Drive Folder files).
objectId: Id of the parent object. You can use 15-character or 18-character Salesforce.com ID.
Return Value: The method will return a list of ResultObject (Figure 8) which holds delete status information for each file record.
...