sha3: move test data to testdata

Change the location of the KAT data for consistency with
other packages.

Change-Id: Ica10ad7d1730603f957fb413e28fe771b3c323bc
Reviewed-on: https://go-review.googlesource.com/3267
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed