QmlJsInspector: remove private header dependencies

A copy of the client debugging code is made in src/libs/qmljsdebugclient/
(this comes from the qt code from commit 65642dd343bf61)

So the qmljsinspector plugin does not require anymore Qt private headers.

src/plugins/debugger/qml/qmlengine.h

@@ -32,10 +32,6 @@
 
 #include "debuggerengine.h"
 
-#include "private/qdeclarativedebug_p.h"
-#include "private/qdeclarativedebugclient_p.h"
-#include "private/qdeclarativeenginedebug_p.h"
-
 #include <QtCore/QByteArray>
 #include <QtCore/QHash>
 #include <QtCore/QObject>
@@ -49,14 +45,6 @@
 #include <QtNetwork/QTcpSocket>
 
 
-QT_BEGIN_NAMESPACE
-class QTcpSocket;
-class QDeclarativeDebugConnection;
-class QDeclarativeEngineDebug;
-class QDeclarativeDebugEnginesQuery;
-class QDeclarativeDebugRootContextQuery;
-QT_END_NAMESPACE
-
 namespace Debugger {
 namespace Internal {