Remove Project::dependsOn(), it's never called

I don't remember why I did leave it alone in the reafctoring some years
ago, but surely it serves no purpose.

Change-Id: Idf920faf3f8f7128cd410501f2c3748e100dfbfb
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>

src/plugins/qmlprojectmanager/qmlproject.h

@@ -74,8 +74,6 @@ public:
     ProjectExplorer::IProjectManager *projectManager() const;
     Internal::QmlProjectTarget *activeTarget() const;
 
-    QList<ProjectExplorer::Project *> dependsOn();
-
     QList<ProjectExplorer::BuildConfigWidget*> subConfigWidgets();
 
     ProjectExplorer::ProjectNode *rootProjectNode() const;