Removed Orkut backend

As of September 30, 2014, Orkut [has been shut down](https://support.google.com/orkut/?hl=en), so there's no need for the corresponding backend anymore.

I think the presence of Orkut might confuse some people, also it might give a wrong impression about the up-to-dateness of this library.
Logging a deprecation-warning might be the better choice though, since it preserves the backward-compatibility. What do you think?