In the twoNonZero function in hash_test, the buffer is sliced as [:] three times. This change deletes them.

Change-Id: I0701d0c810b4f3e267f80133a0dcdb4ed81fe356
Reviewed-on: https://go-review.googlesource.com/c/156138Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>