This reverts commit 836773c0.

Reason for revert: Breaks full-debug support:
https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux%20-%20full%20debug/5493

Original change's description:
> Implement v8::internal::MicrotaskQueue::EnqueueMicrotask
> 
> This adds `queue` and `pending_microtask_count` as members of
> v8::internal::MicrotaskQueue, and implements its EnqueueMicrotask.
> The implementation itself is similar to Isolate::EnqueueMicrotask.
> 
> Bug: v8:8124
> Change-Id: Idb5c50b2add96b72cbe9e36aeec7cb568072f0cb
> Reviewed-on: https://chromium-review.googlesource.com/1205430
> Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55884}

TBR=ulan@chromium.org,adamk@chromium.org,hpayer@chromium.org,tzik@chromium.org

Change-Id: I299884eb6b41fcbff7c486cad636ab7b9821dfe3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8124
Reviewed-on: https://chromium-review.googlesource.com/1225752Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55888}