Revert of [heap] Aggressive code flushing in GC stress mode. (patchset #1 id:1 of https://codereview.chromium.org/1483993002/ )

Reason for revert:
This breaks (surprise) GC stress with custom snapshot, cannot reproduce, will need to investigate further.

https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20GC%20Stress%20-%20custom%20snapshot/builds/2909/steps/Mjsunit/logs/deopt-inlined-from-call

Original issue's description:
> [heap] Aggressive code flushing in GC stress mode.
>
> This disregards the code age heuristic when deciding whether to flush
> code so that GC stress mode is more likely to flush out potential races
> between our various "invariants".
>
> R=hpayer@chromium.org
>
> Committed: https://crrev.com/28a3f23e50f1847dd1152e6bb4aa0579acbdaaab
> Cr-Commit-Position: refs/heads/master@{#32414}

TBR=hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1485823002

Cr-Commit-Position: refs/heads/master@{#32416}