... in favour of RootsTable::IsImmortalImmovable().

Bug: v8:8238
Change-Id: Ic8434a1658b9ba982a93dd268dbfe52a6cc5c6a2
Reviewed-on: https://chromium-review.googlesource.com/c/1270582
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56472}