Kill THCUNN (#63429)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/63429
Test Plan: Imported from OSS
Reviewed By: mruberry
Differential Revision: D30441308
Pulled By: ngimel
fbshipit-source-id: 3ae342a2f8d5c7f8827b637c4055c5d1b0a1be26
