This reverts commit 85bbabd9.

The reverted CL broke all builds, because it depends on other CLs
that haven't been reviewed or landed yet.

Change-Id: I936f969431e0ac77133e43de2bf63042cef6b777
Reviewed-on: https://go-review.googlesource.com/21238Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>