Dont specify sidebar for group and group settings layouts

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/layouts/group.html.haml

 - page_title       @group.name
 - page_description @group.description  unless page_description
 - header_title     group_title(@group) unless header_title
-- sidebar          "dashboard"         unless sidebar
 - nav              "group"
 
 = render template: "layouts/application"

app/views/layouts/group_settings.html.haml

 - page_title    "Settings"
-- sidebar       "dashboard" unless sidebar
 - nav           "group"
 
 = render template: "layouts/group"