This reverts commit 78f8ff95.

Reason for revert: Causing failures on ClusterFuzz and flakes on the waterfall.
BUG: v8:8166, chromium:883042, chromium:883054, chromium:883119, chromium:883110

Original change's description:
> [preparser] Refactor VariableProxies to use ThreadedLists interface
>
> Bug: v8:7926,
> Change-Id: Idfc520b67696c8a838a0ee297ea392d416dd899e
> Reviewed-on: https://chromium-review.googlesource.com/1206292
> Commit-Queue: Florian Sattler <sattlerf@google.com>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55801}

TBR=marja@chromium.org,cbruni@chromium.org,ishell@chromium.org,verwaest@chromium.org,sattlerf@google.com

Change-Id: Ibebff76b5ae69b9790b73c6bd1d53beff5d53673
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7926
Reviewed-on: https://chromium-review.googlesource.com/1221227Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55819}