Remove 'AsyncArrowFunction' test

There is no such hidden constructor, it's the same as the hidden
AsyncFunction constructor. In other words:

```js
Object.getPrototypeOf(async () => {}).constructor ===
Object.getPrototypeOf(async function () {}).constructor
```

Also add a test to ensure that %AsyncFunction.prototype% is indeed the
prototype of an async arrow function.

Closes #4044.

harness/hidden-constructors.js

@@ -5,13 +5,11 @@
 description: |
   Provides uniform access to built-in constructors that are not exposed to the global object.
 defines:
-  - AsyncArrowFunction
   - AsyncFunction
   - AsyncGeneratorFunction
   - GeneratorFunction
 ---*/
 
-var AsyncArrowFunction = Object.getPrototypeOf(async () => {}).constructor;
 var AsyncFunction = Object.getPrototypeOf(async function () {}).constructor;
 var AsyncGeneratorFunction = Object.getPrototypeOf(async function* () {}).constructor;
 var GeneratorFunction = Object.getPrototypeOf(function* () {}).constructor;

test/built-ins/AsyncArrowFunction/is-a-constructor.js

@@ -1,24 +0,0 @@
-// Copyright (C) 2020 Rick Waldron. All rights reserved.
-// This code is governed by the BSD license found in the LICENSE file.
-
-/*---
-esid: sec-ecmascript-standard-built-in-objects
-description: >
-  The AsyncArrowFunction constructor implements [[Construct]]
-info: |
-  IsConstructor ( argument )
-
-  The abstract operation IsConstructor takes argument argument (an ECMAScript language value).
-  It determines if argument is a function object with a [[Construct]] internal method.
-  It performs the following steps when called:
-
-  If Type(argument) is not Object, return false.
-  If argument has a [[Construct]] internal method, return true.
-  Return false.
-includes: [isConstructor.js, hidden-constructors.js]
-features: [Reflect.construct]
----*/
-
-assert.sameValue(isConstructor(AsyncArrowFunction), true, 'isConstructor(AsyncArrowFunction) must return true');
-new AsyncArrowFunction();
-  

test/language/expressions/async-arrow-function/prototype.js

@@ -0,0 +1,17 @@
+// Copyright (C) 2024 Linus Groh. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-async-arrow-function-definitions-runtime-semantics-evaluation
+description: The prototype of an async arrow function is %AsyncFunction.prototype%.
+info: |
+    AsyncArrowFunction : async AsyncArrowBindingIdentifier => AsyncConciseBody
+
+    ...
+    6. Let closure be OrdinaryFunctionCreate(%AsyncFunction.prototype%, sourceText, parameters,
+       AsyncConciseBody, lexical-this, env, privateEnv).
+    ...
+includes: [hidden-constructors.js]
+---*/
+
+assert.sameValue(Object.getPrototypeOf(async () => {}), AsyncFunction.prototype);