remove th_fill and th_mul dead code (#52546)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/52546
Test Plan: Imported from OSS
Reviewed By: ailzhang
Differential Revision: D26654127
Pulled By: malfet
fbshipit-source-id: 68b777cd8ce2992a876dc8d22276a2afcef4830e
