No tests, because tests are in std. (See TestTransportIDNA_h2)

Updates golang/go#13835

Change-Id: I0a327d9652ea5e6f32dfa279550915af61567bed
Reviewed-on: https://go-review.googlesource.com/29071
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>