This reverts commit c48096d4.

Reason for revert: Flaky bot failures (https://bugs.chromium.org/p/v8/issues/detail?id=9744#c9)

Original change's description:
> Reland "[runtime] Remove extension slots from context objects"
> 
> This is a reland of c07c02e1
> 
> Original change's description:
> > [runtime] Remove extension slots from context objects
> >
> > Context objects have an extension slot, which contains further
> > additional data that depends on the type of the context.
> >
> > This CL removes the extension slot from contexts that don't need
> > them, hence reducing memory.
> >
> > The following contexts will still have an extension slot: native,
> > module, await, block and with contexts. See objects/contexts.h for
> > what the slot is used for.
> > The following contexts will not have an extension slot anymore (they
> > were not used before): script, catch and builtin contexts.
> > Eval and function contexts only have the extension slot if they
> > contain a sloppy eval.
> >
> > Bug: v8:9744
> > Change-Id: I8ca56c22fa02437bbac392ea72174ebfca80e030
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1863191
> > Commit-Queue: Victor Gomes <victorgomes@google.com>
> > Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> > Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> > Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> > Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> > Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> > Auto-Submit: Victor Gomes <victorgomes@google.com>
> > Cr-Commit-Position: refs/heads/master@{#64372}
> 
> TBR=verwaest@chromium.org,jgruber@chromium.org,ulan@chromium.org,leszeks@chromium.org,petermarshall@chromium.org
> 
> Bug: v8:9744
> Change-Id: I0749cc2d8f59940c25841736634a70047116d647
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1869192
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Peter Marshall <petermarshall@chromium.org>
> Auto-Submit: Victor Gomes <victorgomes@google.com>
> Cr-Commit-Position: refs/heads/master@{#64380}

TBR=ulan@chromium.org,jgruber@chromium.org,petermarshall@chromium.org,leszeks@chromium.org,verwaest@chromium.org,victorgomes@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:9744
Change-Id: Ia58067b41f1eb5880a52b36ead754d7190ff7f6f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1871922Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64424}