This reverts commit 1186fc50.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20UBSan/16531/overview

Original change's description:
> [heap] Disable the young generation in shared heaps
>
> A shared heap will not have a young generation in the beginning.
>
> Bug: v8:11708
> Change-Id: I947ddb91a23a72a8cee3aa3e554723dda8146011
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2891569
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74697}

Bug: v8:11708
Change-Id: I8de67f70b00b5bd3066659e07fb1fd3ecfb76211
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2909693
Auto-Submit: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#74699}