driver: use the built-in min/max function

Starting from Go 1.21, the min/max functions are built-in.

Therefore, we can remove the custom functions with the same name.

Change-Id: Ie3490436ce36e8548a834628d7a269bf58afbd01
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/707475
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Sean Liao <sean@liao.dev>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>