Stop initializing THNN backend. (#25352)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25352
It doesn't appear to be necessary anymore; assuming this works I'll kill the codegen in a follow-up PR.
Test Plan: Imported from OSS
Differential Revision: D17101573
Pulled By: gchanan
fbshipit-source-id: bd3d1724ee5c659185a161b1e291e30af52f0a8a
