This reverts commit 9afde91b.

Reason for revert:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Arm/builds/6616

Original change's description:
> [builtins] Load external references from the external-reference-table
> 
> Off-heap code cannot embed external references. With this CL, we load
> from the external reference table (reached through the root pointer)
> instead.
> 
> In a follow-up, the table could be stored within the isolate itself,
> removing one more level of indirection.
> 
> Bug: v8:6666
> Change-Id: I4c612ad3d4112ec03c3b389f5bfb9cdc3dc8a671
> Reviewed-on: https://chromium-review.googlesource.com/970468
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52073}

TBR=yangguo@chromium.org,mstarzinger@chromium.org,jgruber@chromium.org

Change-Id: Iecc2a68e54339e153f1d1e882d8972d5c9cff442
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6666
Reviewed-on: https://chromium-review.googlesource.com/971902Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52083}