Remove pinned nav functionality and side_navbar_class

app/helpers/nav_helper.rb

 module NavHelper
-  def page_sidebar_class
-    if pinned_nav?
-      "page-sidebar-expanded page-sidebar-pinned"
-    end
-  end
-
   def page_gutter_class
     if current_path?('merge_requests#show') ||
         current_path?('merge_requests#diffs') ||
@@ -32,10 +26,6 @@ module NavHelper
     class_name = ''
     class_name << " with-horizontal-nav" if defined?(nav) && nav
 
-    if pinned_nav?
-      class_name << " header-sidebar-expanded header-sidebar-pinned"
-    end
-
     class_name
   end
 
@@ -46,8 +36,4 @@ module NavHelper
   def nav_control_class
     "nav-control" if current_user
   end
-
-  def pinned_nav?
-    cookies[:pin_nav] == 'true'
-  end
 end

app/views/layouts/_page.html.haml

-.page-with-sidebar{ class: "#{page_sidebar_class} #{page_gutter_class}" }
-  .sidebar-wrapper.nicescroll
-    .sidebar-action-buttons
-      .nav-header-btn.toggle-nav-collapse{ title: "Open/Close" }
-        %span.sr-only Toggle navigation
-        = icon('bars')
-
-      %div{ class: "nav-header-btn pin-nav-btn has-tooltip #{'is-active' if pinned_nav?} js-nav-pin", title: pinned_nav? ? "Unpin navigation" : "Pin Navigation", data: { placement: 'right', container: 'body' } }
-        %span.sr-only Toggle navigation pinning
-        = icon('fw thumb-tack')
-
-    - if defined?(sidebar) && sidebar
-      = render "layouts/nav/#{sidebar}"
-    - elsif current_user
-      = render 'layouts/nav/dashboard'
-    - else
-      = render 'layouts/nav/explore'
-
+.page-with-sidebar{ class: "#{page_gutter_class}" }
   - if defined?(nav) && nav
     .layout-nav
       .container-fluid