Given that we no longer need to iterate over lists of optimized JS functions 
(c.f. https://chromium-review.googlesource.com/c/v8/v8/+/647596), we can 
remove this field. Thus saving the size of one pointer per function.

Bug: v8:6637
Change-Id: If77951f2eddba33ba350fa9ddf03a4edb3f7c7d8
Reviewed-on: https://chromium-review.googlesource.com/652373Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Juliana Patricia Vicente Franco <jupvfranco@google.com>
Cr-Commit-Position: refs/heads/master@{#47875}