Remove duplicate code

Author: GromNaN

src/DependencyInjection/DoctrineMongoDBExtension.php

@@ -279,10 +279,6 @@ protected function registerMappingDrivers(array $objectManager, ContainerBuilder
                 }
 
                 $mappingDriverDef->setArguments($args);
-            } elseif ($driverType === 'attribute') {
-                $mappingDriverDef = new Definition($this->getMetadataDriverClass($driverType), [
-                    array_values($driverPaths),
-                ]);
             } else {
                 $mappingDriverDef = new Definition($this->getMetadataDriverClass($driverType), [
                     array_values($driverPaths),