crypto: update Hash comments to point to crypto/sha3

crypto: update Hash comments to point to crypto/sha3

Updates #65269

Change-Id: I6a6a6964060f587ec8c918f16b7c776d47e91f5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/701515
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>