LibJS: Remove Object::value_of()

Being really close to Object.prototype.valueOf() name wise makes this
unnecessarily confusing - while it sometimes serves as the
implementation of a valueOf() function, it's an abstraction which the
spec doesn't have.
Use the appropriate getters to retrieve specific internal slots instead,
most commonly [[FooData]] from the primitive wrapper objects.
For the Object class specifically, use the Value(Object*) ctor instead.

Userland/Libraries/LibJS/AST.cpp

@@ -364,7 +364,7 @@ Value SuperCall::execute(Interpreter& interpreter, GlobalObject& global_object)
         return {};
 
     // 5. If IsConstructor(func) is false, throw a TypeError exception.
-    if (!func || !func->value_of().is_constructor()) {
+    if (!func || !Value(func).is_constructor()) {
         vm.throw_exception<TypeError>(global_object, ErrorType::NotAConstructor, "Super constructor");
         return {};
     }