Simplify copy kernel with static_cast_with_inter_type (#29631)
Summary:
After https://github.com/pytorch/pytorch/pull/29612 get merged, `static_cast_with_inter_type` can now automatically convert complex types to its real values, therefore there is no need to do it inside copy kernel.
This should wait until https://github.com/pytorch/pytorch/pull/29612 get merged, otherwise it won't pass CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29631
Differential Revision: D18485676
Pulled By: ezyang
fbshipit-source-id: 0bbfd551e3d3010f87eef0fce23a1f8a094b7d31
