cmd: use built-in min/max instead of bespoke versions

cmd: use built-in min/max instead of bespoke versions

Now that we're bootstrapping from a toolchain that has min/max builtins.

Update #64751

Change-Id: I63eedf3cca00f56f62ca092949cb2dc61db03361
Reviewed-on: https://go-review.googlesource.com/c/go/+/610355
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@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>