Unused codes in `winreg.c`

[aisk]

Bug report

Bug description:

Both PyHKEY_New and PyWinObject_CloseHKEY are unused and not exported to the module, so I think we can safely remove them to clean up the codebase. The latter looks like it was intended to be a module-level function exposed to Python, but it hasn’t been exported in recent versions at least.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-140916: Remove unused codes in winreg.c #140934