Slightly simplify fuzzer_test by using gn's new-ish not_needed() function.

No intended behavior change.

Bug: none
Change-Id: I1191d7dd55108a4ae9fdab19ee299bf6c6c08ec2
Reviewed-on: https://chromium-review.googlesource.com/1055749
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557981}