Some times it's desirable to delete an attachment that has already been uploaded, to delete an attachment, send
a http DELETE command to $filetransfer/attachments/$id where $id is the attachment id.
An example using curl:
curl -s -X DELETE --user "$api_key:x" -H 'Content-Type: text/xml' https://test.host/attachments/123
this will delete attachment with id 123 if the api_key DyTMSdfCduO5l6vfU823AA is valid for the owner or attachment with id 123.