Revert D30426527: Adding DataLoader2 class as future replacement of DataLoader
Test Plan: revert-hammer
Differential Revision:
D30426527 (https://github.com/pytorch/pytorch/commit/5a7133b87fe2fd7d025d36855ed4cc06539a9299)
Original commit changeset: e5905d3364c4
fbshipit-source-id: 794d8a4e9256ccff8cf894aee10eff6adc30d502
