Revert "[d8] Fix a crash when getting the worker's onmessage handler"

This reverts commit a850668ccf.

Reason for revert: new test flaking on many bots, e.g. https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Win32/31068/overview

Original change's description:
> [d8] Fix a crash when getting the worker's onmessage handler
>
> Bug: chromium:1162473
> Change-Id: Ided2f52882aaf02e1dc9a8d0ba883fedf029464d
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2663004
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Commit-Queue: Marja Hölttä <marja@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#72473}

TBR=marja@chromium.org,cbruni@chromium.org

Change-Id: I5ec056185967974a94fd61baec8a75e855e1a272
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1162473, v8:11383
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2666693
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72481}

src/d8/d8.cc

@@ -3547,11 +3547,12 @@ void Worker::ProcessMessage(std::unique_ptr<SerializationData> data) {
   Local<Object> global = context->Global();
 
   // Get the message handler.
-  MaybeLocal<Value> maybe_onmessage = global->Get(
-      context, String::NewFromUtf8Literal(isolate_, "onmessage",
-                                          NewStringType::kInternalized));
-  Local<Value> onmessage;
-  if (!maybe_onmessage.ToLocal(&onmessage) || !onmessage->IsFunction()) {
+  Local<Value> onmessage = global
+                               ->Get(context, String::NewFromUtf8Literal(
+                                                  isolate_, "onmessage",
+                                                  NewStringType::kInternalized))
+                               .ToLocalChecked();
+  if (!onmessage->IsFunction()) {
     return;
   }
   Local<Function> onmessage_fun = onmessage.As<Function>();

test/mjsunit/regress/regress-crbug-1162473.js

@@ -1,7 +0,0 @@
-// Copyright 2021 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-const script = `__proto__ = Realm.global(Realm.create());`;
-const w = new Worker(script, {type : 'string'});
-w.postMessage('hi');