This reverts commit e70cbb83.

Reason for revert: Breaks compile on gcc.
https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20gcc/11148

Original change's description:
> [string] Fix non-SeqStrings in IsEqualTo
>
> Bug: chromium:1193903
> Change-Id: I80704dd3cba5754779432356b20bd3ea99630291
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2794426
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73746}

Bug: chromium:1193903
Change-Id: If700cdc7cf8b50a9430d17489485769cb524efd5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2797539
Auto-Submit: Bill Budge <bbudge@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#73749}