Remove now-redundant `page_description` call from Projects#show

app/views/projects/show.html.haml

-- page_description @project.description
-
 = content_for :meta_tags do
   - if current_user
     = auto_discovery_link_tag(:atom, namespace_project_path(@project.namespace, @project, format: :atom, private_token: current_user.private_token), title: "#{@project.name} activity")