The dir parameter was removed in https://golang.org/cl/5732045.

Fixes #15503.

Change-Id: I02a6d8317233bea08633715a095ea2514822032b
Reviewed-on: https://go-review.googlesource.com/24011
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <shurcool@gmail.com>
Reviewed-by: Andrew Gerrand <adg@golang.org>