fix pow bug on overloads and clean up (#20824)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20824
ghimport-source-id: ceb1b64e2866ec8577800a8c378d8222a62cf199
Reviewed By: cpuhrsch
Differential Revision: D15458009
Pulled By: wanchaol
fbshipit-source-id: 51546d142d2c84e961d8b12ae85a2988a342da3b
