Revert D26644079: [pytorch][PR] Adding functional way of stacking DataPipes
Test Plan: revert-hammer
Differential Revision:
D26644079 (https://github.com/pytorch/pytorch/commit/7972036bbb4b157721f9af800b10b50c8cd31bf3)
Original commit changeset: dcf464637b4f
fbshipit-source-id: a12a06d7e7fb3821a0990bbc6305d02721ead82c
