Building with gccgo failed with an undefined symbol error from an
unnecessary hash function.

Updates #19773

Change-Id: Ic78bf1b086ff5ee26d464089c0e14987d3fe8b02
Reviewed-on: https://go-review.googlesource.com/c/130956
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>