syscall: remove Windows 7 console handle workaround

syscall: remove Windows 7 console handle workaround

Windows 7 is no longer supported, there is no need to complicate the
code to support inheriting console handles.

Change-Id: Ie9f5cde77a63ea4fa6032bbb7ba5bd48a0989c5b
Reviewed-on: https://go-review.googlesource.com/c/go/+/531235
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Quim Muntal <quimmuntal@gmail.com>