syscall: remove unused windows function

syscall: remove unused windows function

It's causing the dependency test to fail.

Fixes #73274

Change-Id: I7d80ea4872e360c16ac3b77acf15fa2660d117b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/663975
Auto-Submit: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>