This reverts commit fac6f63e.

Reason for revert: https://bugs.chromium.org/p/chromium/issues/detail?id=907479

Original change's description:
> Use CopyElements (which uses memcpy) to copy FixedDoubleArray.
> 
> This improves the performance of ExtractFixedArray and
> CloneFastJSArray for double arrays, which in turn improve the
> performance of cloning double arrays with slice() or spreading.
> 
> This, however, does not improve performance of spreading holey
> double arrays, because spreading needs extra work to convert
> holes to undefined.
> 
> Bug: v8:7980
> Change-Id: Ib8aed74abbb0b06982a3b754e134fa415cb7de2d
> Reviewed-on: https://chromium-review.googlesource.com/c/1280308
> Reviewed-by: Michael Stanton <mvstanton@chromium.org>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
> Commit-Queue: Hai Dang <dhai@google.com>
> Cr-Commit-Position: refs/heads/master@{#56680}

TBR=mvstanton@chromium.org,neis@chromium.org,sigurds@chromium.org,dhai@google.com

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

Bug: v8:7980, chromium:907479
Change-Id: Iacf37fa3276345fe8e264fe976d296b015ed6790
Reviewed-on: https://chromium-review.googlesource.com/c/1351003Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57864}