webp: fix tests for webp/nycbcra deprecation.

The previous commit (00fe24ef "webp/nycbcra: deprecate package") was
incomplete.

Change-Id: I6af5e1633b9c291e72b02877b308eae6e5624ef5
Reviewed-on: https://go-review.googlesource.com/21441
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2 files changed