CopyBackward: Remove redundant src_device and unnecessary copy=True (#60025)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60025
`to` already copies unconditionally if `src.device() != options.device()` so
specifying the copy argument is unnecessary.
`src.device()` is also completely equivalent to `src.options().device()` so
storing both is redundant.
Test Plan: Imported from OSS
Reviewed By: zou3519
Differential Revision: D29698627
Pulled By: albanD
fbshipit-source-id: eb091d39b71db688e6bcbb33a227c01b94b432bb
