cmd/compile: clean up debug info generation logging

Remove the unexpected function, which is a lot less relevant now that
the generation basically can't detect invalid states, and make sure no
logging appears without -d locationlists=2.

Updates #25404

Change-Id: If3522df5a7397f2e7b43cb808936e319132132b6
Reviewed-on: https://go-review.googlesource.com/114007


Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>