Vcs: Dissolve VcsManager::registerVersionControl

It's a somewhat unusual pattern, spelling it out will help
to move the vcs plugins setup closer to the now-usual pattern.

Change-Id: Ie7b70e52d75e34cd36b6a1d55ca868e3edab44a7
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/coreplugin/vcsmanager.h

@@ -56,14 +56,6 @@ class CORE_EXPORT VcsManager : public QObject
 public:
     static VcsManager *instance();
 
-    template <typename T, typename... Args>
-    static T *registerVersionControl(Args&&... args)
-    {
-        auto vc = new T(std::forward<Args>(args)...);
-        addVersionControl(vc);
-        return vc;
-    }
-
     static void extensionsInitialized();
 
     static const QList<IVersionControl *> versionControls();
@@ -110,11 +102,11 @@ private:
     explicit VcsManager(QObject *parent = nullptr);
     ~VcsManager() override;
 
+    void handleConfigurationChanges();
     static void addVersionControl(IVersionControl *vc);
 
-    void handleConfigurationChanges();
-
     friend class Core::Internal::MainWindow;
+    friend class Core::IVersionControl;
 };
 
 } // namespace Core