Everything is SSA now.

Update #16357

Change-Id: I436dbe367b863ee81a3695a7d653ba4bfc5b0f6c
Reviewed-on: https://go-review.googlesource.com/29232Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>