The array can be FixedArrayBase, PropertyArray or HeapObject. That
HeapObject has to be either a FixedArray or a PropertyArray since we
have an assert for it. However, due to how the code is structured it
is not so simple to remove HeapObject from the Union.

Drive-by: deleted unused version of BuildFastArrayForEach.

Bug: v8:9708, v8:6949
Change-Id: I980f759dad9c76f0c765622cbdda37e33709f53f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2362954Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69519}