some sshleifer/xsum hub models  have bart-large-cnn task_specific_params['summarization']
S3 only fix! 

Done. <|||||>- [x] pegasus xsum students
- [x] uploaded distilled pegasus
- [x] re-evaluate updated layerdrop model  (te: 23.5291: quickly worsens)
- [x] re-evaluate bart-xsum pseudolabel model(s). 