Fix PHPCR repository class: "Sonata\MediaBundle\PHPCR\GalleryHasMediaRepository" is declared twice

Hello,

I have the following warning since: https://github.com/sonata-project/SonataMediaBundle/commit/0c27e4fff161667f5b0243a16fb867d0f4297fe2

Warning: Ambiguous class resolution, "Sonata\MediaBundle\PHPCR\GalleryHasMediaRepository" was found in both "/var/lib/jenkins/workspace/monclubbusiness/vendor/sonata-project/media-bundle/PHPCR/BaseGalleryHasMediaRepository.php" and "/var/lib/jenkins/workspace/monclubbusiness/vendor/sonata-project/media-bundle/PHPCR/BaseGalleryRepository.php", the first will be used.

Effectively the class "Sonata\MediaBundle\PHPCR\GalleryHasMediaRepository" is declared twice.