Migrate THCCachingHostAllocator to ATen (#65746)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65746
This also removes the cudaHostAllocator field on THCState, since there
doesn't seem to be an API anywhere for customizing it.
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D31236630
Pulled By: ngimel
fbshipit-source-id: 2a8e756222ae70565e77f8e7139d60ec5be32276
