Simplify scalar_check of nll_loss. (#30669)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30669
The inputs can't be 0-d, so we don't need that check in the scalar_check.
Test Plan: Imported from OSS
Differential Revision: D18784524
Pulled By: gchanan
fbshipit-source-id: d44222dffc91880a6e8c7be69e6e146e60040d43
