remove cadd_avx2 dead code (#34883)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/34883
Test Plan: Imported from OSS
Differential Revision: D20611526
Pulled By: ngimel
fbshipit-source-id: 78c80b7361119fc8d2b9f6b4f0c86b61723fe05d
