LibJS: Remove non-spec compliant code from internal_construct

It seems that we are now spec compliant enough to be able to remove this
code block :^)

Diff Tests:
    +2 ✅    -2 ❌

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -506,15 +506,6 @@ ThrowCompletionOr<NonnullGCPtr<Object>> ECMAScriptFunctionObject::internal_const
 
     // 10. If result.[[Type]] is return, then
     if (result.type() == Completion::Type::Return) {
-        // FIXME: This is leftover from untangling the call/construct mess - doesn't belong here in any way, but removing it breaks derived classes.
-        // Likely fixed by making ClassDefinitionEvaluation fully spec compliant.
-        if (kind == ConstructorKind::Derived && result.value()->is_object()) {
-            auto prototype = TRY(new_target.get(vm.names.prototype));
-            if (prototype.is_object())
-                TRY(result.value()->as_object().internal_set_prototype_of(&prototype.as_object()));
-        }
-        // EOF (End of FIXME)
-
         // a. If Type(result.[[Value]]) is Object, return result.[[Value]].
         if (result.value()->is_object())
             return result.value()->as_object();

Userland/Libraries/LibJS/Tests/classes/class-inheritance.js

@@ -506,3 +506,29 @@ test("When no constructor on deriving class @@iterator of %Array.prototype% is n
 
     expect(calls).toBe(1);
 });
+
+test("constructor return value overrides inheritance and property initialization", () => {
+    let calls = 0;
+    class Base {
+        constructor() {
+            this.prop = 1;
+            calls++;
+        }
+    }
+
+    class Derived extends Base {
+        constructor() {
+            super();
+
+            // Return an empty object instead of Derived/Base object
+            return {};
+        }
+    }
+
+    let object = new Derived();
+
+    expect(calls).toBe(1);
+    expect(typeof object.prop).toBe("undefined");
+    expect(object instanceof Derived).toBe(false);
+    expect(object instanceof Base).toBe(false);
+});