Removing the temporarily duplicated classes FixedArrayPtr and
FixedArrayBasePtr.

Bug: v8:3770
Change-Id: I056ad74ff69593e9f134ef5c976766812c4d9275
Reviewed-on: https://chromium-review.googlesource.com/c/1345913
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57807}