The duff device has been dropped on loong64,
now we can remove related documentation.
Change-Id: I0bd721adc227522ae3c56dfe199ef735cfdf5d33
Reviewed-on: https://go-review.googlesource.com/c/go/+/740260
Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@golang.org>