Deprecate AMQPQueue::declare() and AMQPExchange::declare() methods

`declare` is a reserved token in PHP and can therefore not be overloaded in userland. Try this snippet:

```php
<?php
class Klass
{
    public function declare()
    {}
}
```

We already have `AMQPExchange::declareExchange()` and `AMQPQueue::declareQueue()` as the main methods.