Move scalar_to_tensor_default_dtype out of ScalarOps.h because it's only useful for torch.where. (#50111)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50111
Test Plan: Imported from OSS
Reviewed By: mruberry
Differential Revision: D25789638
Pulled By: gchanan
fbshipit-source-id: 4254e11e08606b64e393433ef2c169889ff2ac07
