Mercurial: Adapt to 8097879d6d

Make use of VCS base class.

src/plugins/mercurial/mercurialcontrol.h

@@ -50,8 +50,6 @@ public:
     explicit MercurialControl(MercurialClient *mercurialClient);
 
     QString name() const;
-    bool isEnabled() const;
-    void setEnabled(bool enabled);
     bool managesDirectory(const QString &filename) const;
     QString findTopLevelForDirectory(const QString &directory) const;
     bool supportsOperation(Operation operation) const;
@@ -66,9 +64,6 @@ public slots:
     // String -> repository, StringList -> files
     void changed(const QVariant&);
 
-signals:
-    void enabledChanged(bool);
-
 private:
     MercurialClient *mercurialClient;
     bool mercurialEnabled;