iOS: Use an aspect for the executable

More standard pattern nowadays.

Change-Id: I1237555b44fb0a9a6faca086254c49b70c39c3b6
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>

src/plugins/ios/iosrunconfiguration.h

@@ -61,9 +61,6 @@ public:
     bool fromMap(const QVariantMap &map) override;
     QVariantMap toMap() const override;
 
-signals:
-    void localExecutableChanged();
-
 private:
     void deviceChanges();
     friend class IosRunConfigurationWidget;