[calamares] Do not attempt to center Calamares window

- this isn't really a Calamares thing to decide, and anyway centering
   on the desktop is kind of weird in multi-monitor setups and the
   DesktopWidget is deprecated as well.

src/calamares/CalamaresApplication.cpp

@@ -357,8 +357,6 @@ CalamaresApplication::initView()
 
     QTimer::singleShot( 0, m_moduleManager, &Calamares::ModuleManager::loadModules );
 
-    m_mainwindow->move( this->desktop()->availableGeometry().center() - m_mainwindow->rect().center() );
-
     cDebug() << "STARTUP: CalamaresWindow created; loadModules started";
 }