Remove destructor

[donatj]

This destructor isn't actually doing anything because the local variables $clientId and $clientSecret are not defined in this scope.

I think the code intends to be doing the following

        function __destruct()
        {
            unset($this->clientId);
            unset($this->clientSecret);
        }

but that shouldn't be necessary, because the members attached to the class will be unset immediately following destruction.