cmd: replace many sort.Interface with slices.Sort and SortFunc

cmd: replace many sort.Interface with slices.Sort and SortFunc

with slices there's no need to implement sort.Interface

Change-Id: I59167e78881cb1df89a71e33d738d6aeca7adb71
GitHub-Last-Rev: 507ba84453f7305b6b2bf6317292111c00c93ffe
GitHub-Pull-Request: golang/go#68724
Reviewed-on: https://go-review.googlesource.com/c/go/+/602895
Reviewed-by: Ian Lance Taylor <iant@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>