This reverts commit b271ea3c.

Reason for revert: breaks arm build:
https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20arm64%20-%20sim%20-%20debug/17575

Original change's description:
> [ptr-compr] Disable double fields unboxing
> 
> Double field unboxing optimization is incompatible with pointer compression so
> we land this CL before enabling pointer compression in order to separate memory
> and performance regressions caused by disabled double field unboxing from
> pointer compression change.
> 
> Bug: v8:9799
> Change-Id: Ic8118356496a3f351344215b409f9722de6c9355
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1835546
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64089}

TBR=ishell@chromium.org,verwaest@chromium.org

Change-Id: Ief07d8d4b3c4a6f1439656f31b8d34ec99bf9747
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:9799
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1834769Reviewed-by: Francis McCabe <fgm@chromium.org>
Commit-Queue: Francis McCabe <fgm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64090}