This reverts commit f8184738.

Reason for revert: arm is still unhappy https://build.chromium.org/p/client.v8.ports/builders/V8%20Arm%20GC%20Stress/builds/6633

Original change's description:
> Reland "[builtins] Load external references from the external-reference-table"
> 
> This is a reland of 9afde91b
> 
> 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=mstarzinger@chromium.org
> 
> Bug: v8:6666, v8:7580
> Change-Id: I163cfc15605c1183b79ead77df0e37d71d60b6f7
> Reviewed-on: https://chromium-review.googlesource.com/972821
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52118}

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

Change-Id: I5bcd1a1c84c6e9a6a24364390c9359d43c77120d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6666, v8:7580
Reviewed-on: https://chromium-review.googlesource.com/973782Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52121}