Revert "MOB-8620: Map USB_CANCELED_ERROR to ERROR_CANCELLED"

This reverts commit f72eb1ccee6ffdfed8ad285590c4e5b53999ab4f.
MOB-8620: MAP USB_CANCELED_ERROR to ERROR_CANCELLED

This commit updates Transfer::TranslateError() to not report
ERROR_INTERNAL_ERROR for transfers that complete with USB_CANCELED_ERROR.
If bytes have been successfully transferred, ERROR_SUCCESS is reported,
and clients will observe a short transfer. If no bytes have been transferred,
then ERROR_CANCELLED is reported. Client documentation has been updated
to clarify the result given for cancelled transfers.