Remove unnecessary includes and headers from THCCachingAllocator, move to at::cuda:: namespace (#16117)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16117
This means I can move it to c10_cuda with minimal fuss.
Reviewed By: smessmer
Differential Revision: D13717836
fbshipit-source-id: a94c7dc649af64542480fc1c226b289588886c00
