Remove obsolete powerup loading

Powerup data is loaded before each race when the number of karts (and type of race) is known.

src/graphics/irr_driver.cpp

@@ -942,7 +942,6 @@ void IrrDriver::applyResolutionSettings()
         material_manager->addSharedMaterial(materials_file);
     }
 
-    powerup_manager->loadAllPowerups ();
     ItemManager::loadDefaultItemMeshes();
     projectile_manager->loadData();
     Referee::init();