Unfortunately, we still have to keep the field because GC mole and Torque
do not support platform specific padding well
(see http://crbug.com/v8/9287).

Bug: v8:9183
Change-Id: I2210be4b8174c97bc82145605f9b862aac3bdc37
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624791Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61802}