The dummy implementation was causing lots of argument lists
to be prepared and thrown away.

Change-Id: Id0040dec6b0937f3daa8a8d8911fa3280123e863
Reviewed-on: https://go-review.googlesource.com/5700Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>