This flag lost its usefulness in CL 34273.

Change-Id: I033c29f105937139b4e359a340906be439f1ed07
Reviewed-on: https://go-review.googlesource.com/c/141646
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>