Contao\Model\Registry::unregister PHP Method

    public function unregister(Model $objModel)
    {
        $intObjectId = spl_object_hash($objModel);
        // The model is not registered
        if (!isset($this->arrIdentities[$intObjectId])) {
            return;
        }
        $strTable = $objModel->getTable();
        $strPk = $objModel->getPk();
        $intPk = $objModel->{$strPk};
        unset($this->arrIdentities[$intObjectId]);
        unset($this->arrRegistry[$strTable][$intPk]);
        // Allow the model to modify the registry
        $objModel->onUnregister($this);
    }