Deprecated comment.

I believe the hiera backend `module_data` has been introduced in 0.1 and then dropped again in 0.2 (I don't know why exactly).

Is this correct ?

Anyhow, there is no `data` directory anymore. Please update the docs. I am not sure I can really trust any comment now ?
Merge pull request #508 from PierreR/patch-2

Remove deprecated comment