cmd: re-generate all stringer files

cmd: re-generate all stringer files

The tool has gotten better over time, so re-generating the files brings
some advantages like fewer objects, dropping the use of fmt, and
dropping unnecessary bounds checks.

While at it, add the missing go:generate line for obj.AddrType.

Change-Id: I120c9795ee8faddf5961ff0384b9dcaf58d831ff
Reviewed-on: https://go-review.googlesource.com/100015
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>