ProjectNodes: Move vcsTopic to where it belongs

It's a nonsensical operation on anything but ProjectNodes

Change-Id: Id02682e6dde99c5a08362dac0f6286282cfc15b6
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/projectexplorer/projectnodes.cpp

@@ -145,11 +145,6 @@ QString Node::displayName() const
     return QFileInfo(path()).fileName();
 }
 
-QString Node::vcsTopic() const
-{
-    return QString();
-}
-
 QString Node::tooltip() const
 {
     return QDir::toNativeSeparators(path());