Move std and var tests to OpInfos (#50901)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50901
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D26083289
Pulled By: mruberry
fbshipit-source-id: 7e14ff37bba46dd456e0bc0aa9c4e0a632d0734c
