Revert "Fix crash for newly added project nodes"

Actually that's not correct, the projectNode() of ProjectNodes is set in
the constructor to "this".
This reverts commit 123e2b6c.

src/plugins/projectexplorer/projectnodes.cpp

@@ -316,8 +316,6 @@ void ProjectNode::addProjectNodes(const QList<ProjectNode*> &subProjects)
             QTC_ASSERT(!project->parentFolderNode(),
                 qDebug("Project node has already a parent"));
             project->setParentFolderNode(this);
-            project->setProjectNode(this);
-
             foreach (NodesWatcher *watcher, m_watchers)
                 project->registerWatcher(watcher);
             m_subFolderNodes.append(project);