Remove THCudaMemGetInfo. Use c10's cacheInfo instead. (#37447)
Summary:
`THCudaMemGetInfo` has only been used in `aten/src/ATen/native/cudnn/Conv.cpp`. We can extract `c10::cuda::CUDACachingAllocator::cacheInfo` out from it and use it in `aten/src/ATen/native/cudnn/Conv.cpp` directly and drop lines that are not used in `THCudaMemGetInfo`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37447
Differential Revision: D21302770
Pulled By: ezyang
fbshipit-source-id: 41ad68b8fd5ecc7bc666a6861789c6c1f743f420
