This reverts commit 7ae30cb7.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Presubmit/10185

Original change's description:
> [heap] Skip memory reducer on AdjustAmountOfExternalAllocateMemory
> 
> V8 performs GC based on external memory limit. Additionally triggering
> memory reducing GCs may be problematic for large heaps and increases
> the chances of multiple V8 isolates performing GCs after
> IsolateInBackgroundNotification.
> 
> Bug: chromium:1072746
> 
> Change-Id: I7649a176504803ba666e6367b008593bbcfe6312
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2159488
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67398}

TBR=ulan@chromium.org,hpayer@chromium.org,mlippautz@chromium.org

Change-Id: I008b1a0db2b4902190a6fa7e0861b5366f25b7fd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1072746
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2168113Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67400}