Delete torch/csrc/nn/type_checks, which aren't used anymore.
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/25506
Test Plan: Imported from OSS
Differential Revision: D17141960
Pulled By: gchanan
fbshipit-source-id: 460d6a83c796f0d1ca576a709c298e90204f6b06
