Qml Debugger: Eliminate client state callback

The sender()/qobject_cast construct is ugly, unnecessary and it doesn't
work if the method is called directly, rather than through a signal.

Change-Id: I0ac09ad04b956fb4cac38a89162a9dc0055d1831
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/debugger/qml/qmlengine.h

@@ -135,7 +135,6 @@ private:
     void connectionErrorOccurred(QAbstractSocket::SocketError socketError);
     void connectionStateChanged(QAbstractSocket::SocketState socketState);
 
-    void clientStateChanged(QmlDebug::QmlDebugClient::State state);
     void checkConnectionState();
     void showConnectionStateMessage(const QString &message);
     bool isConnected() const;