Inside of V8 there's no use of InternalPackedArray left, so no need to
keep that around.

R=yangguo@chromium.org

Change-Id: I819fc400ef46353339596dec98b70df2d442ed47
Reviewed-on: https://chromium-review.googlesource.com/583653Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46853}