Clean up some imports in cuda kernel code. (#47400)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47400
Test Plan: Imported from OSS
Reviewed By: mruberry
Differential Revision: D24740655
Pulled By: gchanan
fbshipit-source-id: b56a602637c375575444c074c4be0a698441a4ab
