Remove unused files from THNN and THCUNN (#24820)
Summary:
Spin-off from https://github.com/pytorch/pytorch/issues/24818.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24820
Differential Revision: D16890917
Pulled By: ezyang
fbshipit-source-id: 88df6d3ba98600acc810eda406daa1d850ed3320
