Fewer torch.hub requirements (#959)
Fewer torch.hub requirements (#959)

Summary:
We will raise exceptions if these are needed and aren't available. Only keep minimum set of reqs
Pull Request resolved: https://github.com/pytorch/fairseq/pull/959

Differential Revision: D16623304

Pulled By: myleott

fbshipit-source-id: 8e65253742e393b527e8396a9433e64ebec9bb55

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq