Fixed constructor of S3 Adapter: third argument is not needed and will fail if provided

To initialize a connection to S3 is this implementation a region is not used
and will fail because the abstract class `AbstractAmazon` expects a
HttpClient instance as third argument. 

To define the region of a bucket use

    $service = new \ZendService\Amazon\S3\S3("***", "****");
    $service->createBucket("yourbucket", "EU");