We removed calls from our code to Rugged::Repository#fetch_attributes:
<https://gitlab.com/gitlab-org/gitlab_git/commit/340e111e040ae847b614d35b4d3173ec48329015>

However, we didn't remove calls from within Linguist. This method is only called
when calculating the languages for a repository on the Charts page:
<https://github.com/github/linguist/blob/v4.7.0/lib/linguist/lazy_blob.rb#L33-L36>

We can safely use our own Gitlab::Git::Attributes here. On staging, for the
GitLab CE repo, this makes the calculation take about a third of the time:

    # Before
    Benchmark.realtime do
      Linguist::Repository.new(repository.rugged,
                               repository.rugged.head.target_id).languages
    end
    #=> 23.67193900188431

    # After
    Benchmark.realtime do
      Linguist::Repository.new(repository.rugged,
                               repository.rugged.head.target_id).languages
    end
    #=> 8.945212290156633