remove unused THCBlas (#49725)
Summary:
removes unused THCBlas, call `at::cuda::blas::gemm` directly where needed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49725
Reviewed By: mruberry
Differential Revision: D25680831
Pulled By: ngimel
fbshipit-source-id: d826f3f558b156f45f2a4864daf3f6d086bda78c
