This reverts commit 14108f4c.

Reason for revert: Not the culprit for Canary microtask crashes

Original change's description:
> [builtins] Mega-revert to address the Dev blocker in crbug.com/808911.
> 
> - Revert "[builtins] Save one word in contexts for Promise.all."
>   This reverts commit 7632da06.
> - Revert "[builtins] Also use the Promise#then protector for Promise#finally()."
>   This reverts commit d4f072ce.
> - Revert "[builtins] Don't mess with entered context for MicrotaskCallbacks."
>   This reverts commit 6703dacd.
> - Revert "[debugger] Properly deal with settled promises in catch prediction."
>   This reverts commit 40dd0658.
> - Revert "[builtins] Widen the fast-path for Promise builtins."
>   This reverts commit db0556b7.
> - Revert "[builtins] Unify PerformPromiseThen and optimize it with TurboFan."
>   This reverts commit a582199c.
> - Revert "[builtins] Remove obsolete PromiseBuiltinsAssembler::AppendPromiseCallback."
>   This reverts commit 6bf88852.
> - Revert "[builtins] Turn NewPromiseCapability into a proper builtin."
>   This reverts commit 313b490d.
> - Revert "[builtins] Inline InternalPromiseThen into it's only caller"
>   This reverts commit f7bd6a2f.
> - Revert "[builtins] Implement Promise#catch by really calling into Promise#then."
>   This reverts commit b23b098f.
> - Revert "[promise] Remove incorrect fast path"
>   This reverts commit 0f6eafe8.
> - Revert "[builtins] Squeeze JSPromise::result and JSPromise::reactions into a single field."
>   This reverts commit 8a677a28.
> - Revert "[builtins] Refactor promises to reduce GC overhead."
>   This reverts commit 8e7737cb.
> 
> Tbr: hpayer@chromium.org
> Bug: chromium:800651, chromium:808911, v8:5691, v8:7253
> Change-Id: I8c8ea5ed32ed62f6cd8b0d027a3707ddd891e5f1
> Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
> Reviewed-on: https://chromium-review.googlesource.com/906991
> Commit-Queue: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Adam Klein <adamk@chromium.org>
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51158}

Change-Id: I09d958cbebd635a325809072a290f2f53df8c5d4
Tbr: adamk@chromium.org,yangguo@chromium.org,bmeurer@chromium.org
Bug: chromium:800651, chromium:808911, v8:5691, v8:7253
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/908988Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51181}