helloworld-gae-launch-dataflow uses a deperatected library

[lesv]

While working on #589 I found that this sample is using:

    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>gcloud-java</artifactId>
      <version>0.2.8</version>
    </dependency>

Which is most definitely deprecated - wish we could flag.

I quick cs/ internally shows that the sample isn't being used in docs, so I'm going to remove it.