Since the registration requires calling into the library, there's no
reason to get the heap through a magic getter on API level.

Bug: chromium:1056170
Change-Id: I8d2b1d0fcee8c855908bd26c71a22826c493ed29
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2238568
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68315}