remove few unused windows ffi fn

[klensy]

They look unused, so clean up.

[github-actions[bot]]

Code size changes for a hello-world Rust program linked with libstd with backtrace:

On platform windows-latest:

• Original binary size: 138,752 B
• Updated binary size: 137,216 B
• Difference: -1,536 B (-1.11%)