Avoid extended array directly in tests.

Unfortunately, `class Foo extends Array{}` doesn't work well with older
browsers (and would even require changes in our transpilation for
production builds for modern ones).

The actual test doesn't care if its running on an Array (without the
fixes in this PR this modified test still fails the same way).

packages/@ember/-internals/runtime/tests/array/apply-test.js

@@ -3,18 +3,15 @@ import { AbstractTestCase, moduleFor } from 'internal-test-helpers';
 
 class ArrayPrototypeExtensionSelfReferenceTests extends AbstractTestCase {
   '@test should not create non-Symbol, enumerable properties that refer to itself'() {
-    // Don't want to pollute Array.prototype so we make our own to extend
-    class ThrowAwayArray extends Array {}
+    // Don't want to pollute Array.prototype so we make a fake / simple prototype
+    function ThrowAwayArray() {}
 
     // Extend our throw-away prototype (like EXTEND_PROTOTYPES.Array would)
     NativeArray.apply(ThrowAwayArray.prototype);
 
     // Create an instance to test
     let obj = new ThrowAwayArray();
 
-    // Make sure we have an array-like thing & avoid the zero assertion problem is there are no enumerable properties
-    this.assert.strictEqual(obj.length, 0);
-
     // Make sure that no enumerable properties refer back to the object (creating a cyclic structure)
     for (let p in obj) {
       this.assert.notStrictEqual(