Revert of [heap] Do not invoke GC to make heap iterable. (patchset #5 id:80001 of https://codereview.chromium.org/1961373003/ )

Reason for revert:
Breaks https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20gc%20stress/builds/3551

Original issue's description:
> [heap] Do not invoke GC to make heap iterable.
>
> Remove kMakeHeapIterableMask since the heap is always iterable.
>
> BUG=chromium:580959
> LOG=n
>
> Committed: https://crrev.com/7c1cac4888a248fda3fa6de3624f32a6babb37e9
> Cr-Commit-Position: refs/heads/master@{#36333}

TBR=ulan@chromium.org,yangguo@chromium.org,hpayer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:580959

Review-Url: https://codereview.chromium.org/1987363002
Cr-Commit-Position: refs/heads/master@{#36335}