VCS: Speed up

Do not listen on ICore::contextChanged to update actions
(became slow after additional contexts).
git: Make code to find top level faster, avoid
constructing file info lists.
Acked-by: con

src/plugins/git/gitclient.h

@@ -75,7 +75,6 @@ public:
     bool managesDirectory(const QString &) const { return false; }
     QString findTopLevelForDirectory(const QString &) const { return QString(); }
 
-    static QString findRepositoryForFile(const QString &fileName);
     static QString findRepositoryForDirectory(const QString &dir);
 
     void diff(const QString &workingDirectory, const QStringList &diffArgs, const QString &fileName);