generate_jni_registrations: Use @JniIgnoreNatives rather a GN blacklist

Change motivated by JNI refactorings, which are made simpler by not
having to specify this blacklist in GN.

TBR=agrieve  # Trivial build refactor

Bug: 898261
Change-Id: Ic81e99a460f54e5c02fedfd9f8467390045ee21c
Reviewed-on: https://chromium-review.googlesource.com/c/1317341
Commit-Queue: agrieve <agrieve@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605778}
9 files changed