Remove a deprecated feature of GitLab

[harupong]

We are also removing Wall from projects because we feel that the time needed for developing and keeping bug free is not justified if compared to the usefulness of the feature.
GitLab Blog | GitLab 7.0 released with drag and drop images and performance improvements

closes progit/progit2-ja#18

[ben]

Nice catch, thanks. The new flow is a little awkward, though:

This section has focused mainly on the Git-related parts of GitLab, but it's a fairly mature system, and provides many other features that can help your team work together. These include project wikis and system maintenance tools.

Let's change it to this:

This section is focused mainly on the Git-related features of GitLab, but as a mature project, it provides many other features to help your team work together, such as project wikis and system maintenance tools.

…or something similar.

[harupong]

Thanks. I added new commit with your change.

It's kinda hard for non-native English speakers like me to notice/feel the awkwardness in this 😞

[ben]

I completely understand, and we really appreciate the contribution. Thanks!