Android: Switch ContentShell to use implicit JNI registration

Explicit registration is needed only when using the custom linker.
Content shell doesn't use the custom linker, so has no need to jump
through the extra hoops involved with explicit registration.

Change motivated by JNI refactorings, which are made simpler by having
fewer targets use manual JNI registration.

Bug: 898261
Change-Id: Ia38529c1df92264781ba64235a7aea749ef0356a
Reviewed-on: https://chromium-review.googlesource.com/c/1317338
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605344}
3 files changed