Simplify RefCounted check in free()

[KoBeWi]

Use the is_ref_counted() method, which does a simple bool check, instead of casting.

[akien-mga]

Are we confident that this is always in sync for any Object?

[KoBeWi]

It's initialized directly in the RefCounted constructor:

godot/core/object/ref_counted.cpp

Lines 96 to 97 in 1952f64

	RefCounted::RefCounted() :
	Object(true) {

godot/core/object/object.cpp

Lines 1958 to 1963 in 1952f64

	Object::Object(bool p_reference) {
	_construct_object(p_reference);
	}
	Object::Object() {
	_construct_object(false);

No other class overrides it, so it's safe to rely on.

[akien-mga]

Thanks!