runtime: remove remaining windows/arm files and comments

runtime: remove remaining windows/arm files and comments

CL 648795 deleted most of windows/arm code, but some files escaped from
the purge.

This CL finishes the job.

For #71671

Change-Id: Id454c40a673a1a2a9f190d79248e6d56104cdd61
Reviewed-on: https://go-review.googlesource.com/c/go/+/698036
Reviewed-by: qiu laidongfeng <2645477756@qq.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>