This reverts commit 3f22832b.

Reason for revert: Layout tests:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/16849

Original change's description:
> [builtins] Port Map and Set iterators to CodeStubAssembler.
> 
> This is the next step towards faster Map and Set iteration. It
> introduces the appropriate instance types for Map and Set
> iterators (following the pattern for Array iterators) and migrates
> the following builtins to the CodeStubAssembler:
> 
>   - Set.prototype.entries
>   - Set.prototype.values
>   - Map.prototype.entries
>   - Map.prototype.keys
>   - Map.prototype.values
>   - %SetIteratorPrototype%.next
>   - %MapIteratorPrototype%.next
> 
> This already provides a significant performance boost for regular
> for-of iteration of Sets and Maps, by a factor of 5-10 depending
> on the input. The final step will be to inline some fast-paths
> into TurboFan.
> 
> Drive-by-fix: Remove obsolete %IsJSSetIterator and %IsJSMapIterator
> intrinsics and runtime functions.
> 
> Bug: v8:6571, chromium:740122
> Change-Id: Iad7a7dec643d8f8b5799327f89a351108ae856bf
> Reviewed-on: https://chromium-review.googlesource.com/563399
> Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46492}

TBR=jgruber@chromium.org,bmeurer@chromium.org

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

Bug: v8:6571, chromium:740122
Change-Id: Iadb48d72e3b85ec8ad880e50ab7912c5502caf07
Reviewed-on: https://chromium-review.googlesource.com/564419Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46495}