cpu: roll back "use IsProcessorFeaturePresent to calculate ARM64 on windows"

Roll back CL 740880 (commit fc646e489fd944b6f77d327ab77f1a4bab81d5ad)
because it adds a golang.org/x/sys/windows import to the cpu package.
The cpu package is vendored into the main Go tree and the policy there
does not currently permit this dependency.

For golang/go#76791.
Fixes golang/go#78259.

Change-Id: I72860cdf98192f4cbd2b3398926203a752d8d0fe
Cq-Include-Trybots: luci.golang.try:x_sys-gotip-windows-arm64
Reviewed-on: https://go-review.googlesource.com/c/sys/+/757482
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>