Fix wrong class names in SQLAzureFederationsSynchronizer

There is a wrong import in this class:

    use Doctrine\DBAL\Sharding\SingleDatabaseSynchronizer;

Should be:

    use Doctrine\DBAL\Schema\Synchronizer\SingleDatabaseSynchronizer;

The following import is also missing:

    use Doctrine\DBAL\Schema\Synchronizer\SchemaSynchronizer;

This PR fixes them.