[DataPipe] adding/removing __len__ for different DataPipe (#64398)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64398
cc VitalyFedyunin ejguan
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D30710437
Pulled By: NivekT
fbshipit-source-id: 524eda43a2faa0db0c1a662bf9bb4283f0ade83c
