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/perforce/perforceplugin.cpp

@@ -182,7 +182,8 @@ bool PerforcePlugin::initialize(const QStringList & /* arguments */, QString *er
     Q_UNUSED(errorMessage)
     Context context(PERFORCE_CONTEXT);
 
-    initializeVcs<PerforceVersionControl>(context, this);
+    auto vcsCtrl = new PerforceVersionControl(this);
+    initializeVcs(vcsCtrl, context);
 
     m_instance = this;