yii\mongodb\Migration::dropIndex PHP Method

    public function dropIndex($collection, $columns)
    {
        $this->beginProfile($token = "    > drop index on " . $this->composeCollectionLogName($collection) . " (" . Json::encode((array) $columns) . ") ...");
        $this->db->getCollection($collection)->dropIndex($columns);
        $this->endProfile($token);
    }