ProjectExplorer: Remove arguments from node change signals

This discourages storing the pointers needlessly. The items
are still easy accessible by the static ProjectTree::currentNode()

Change-Id: I3c0cd019e9fdc382afacbc9d9de3b97d5f58ae1e
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/projecttree.cpp

@@ -222,10 +222,9 @@ void ProjectTree::update(Node *node, Project *project)
 
     if (changedNode) {
         m_currentNode = node;
-        emit currentNodeChanged(m_currentNode, project);
+        emit currentNodeChanged();
     }
 
-
     if (changedProject) {
         emit currentProjectChanged(m_currentProject);
         sessionChanged();