This function deletes download by id.
Doesn't return any data.
jetapi backup -F deleteDownload -D '_id=5b681559d5ac5e601054c2c3'
https://hostname.example.com:2087/cpsess##########/cgi/addons/jetbackup/api.cgi?function=deleteDownload&_id=5b681559d5ac5e601054c2c3