Issue with test set in CASIA-SURF HLDI

https://gitlab.idiap.ch/bob/bob.pad.face/blob/master/bob/pad/face/database/casiasurf.py#L178

'unknown' is not needed anymore right? Also https://gitlab.idiap.ch/bob/bob.pad.face/blob/master/bob/pad/face/database/casiasurf.py#L44 the .attack_type labels.