crypto/x509: use syscall.GetVersion instead of internal/syscall/windows.GetVersion

crypto/x509: use syscall.GetVersion instead of internal/syscall/windows.GetVersion

cl8167 introduced internal/syscall/windows.GetVersion, but we already
have that function in syscall.GetVersion. Use that instead.
Also revert all internal/syscall/windows cl8167 changes.

Change-Id: I512a5bf4b3b696e93aaf69e9e8b7df7022670ec0
Reviewed-on: https://go-review.googlesource.com/8302
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Minux Ma <minux@golang.org>