As the title stated.
**Changes:**
- Remove unnecessary header file
- Remove unnecessary registry logic about PrivateUse1HooksRegistry,such as TORCH_DECLARE_REGISTRY, C10_DEFINE_REGISTRY, etc,.
- using static + global variable to do initialization instead of call_one
**Next Step:**
Enable test_openreg.py in CI/CD to guard the quality of PrivateUse1
Pull Request resolved: https://github.com/pytorch/pytorch/pull/151005
Approved by: https://github.com/albanD