EventSource: make eventSourceDeRegisteredForResource a default method

The EventSource is defined as follow:

```java
public interface EventSource extends Closeable {
    default void start() {
    }

    default void close() {
    }

    void setEventHandler(EventHandler var1);

    void eventSourceDeRegisteredForResource(String var1);
}
```

I think that eventSourceDeRegisteredForResource should be make as a default method.
