Remove many unused bfloat16 functions in TH
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/30329
Test Plan: Imported from OSS
Differential Revision: D18764281
Pulled By: VitalyFedyunin
fbshipit-source-id: bc3f91c6d09d4f73c77fe1492a358128744aee76
