Super nav header: Remove unused styles

These seem to be from previous iterations of the markup and haven't been
removed.

app/assets/stylesheets/govuk_publishing_components/components/_layout-super-navigation-header.scss

@@ -379,17 +379,6 @@ $after-button-padding-left: govuk-spacing(4);
   display: none;
 }
 
-// Search and popular content dropdown.
-.gem-c-layout-super-navigation-header__search-and-popular {
-  display: none;
-  padding-bottom: govuk-spacing(4);
-  padding-top: govuk-spacing(4);
-
-  .js-module-initialised & {
-    display: block;
-  }
-}
-
 // Styles for top level navigation toggle button.
 .gem-c-layout-super-navigation-header__navigation-top-toggle-button {
   font-size: 16px;
@@ -780,16 +769,6 @@ $after-button-padding-left: govuk-spacing(4);
   }
 }
 
-// Dropdown menu description.
-.gem-c-layout-super-navigation-header__menu-description {
-  display: none;
-
-  @include govuk-media-query($from: "desktop") {
-    display: block;
-    padding: govuk-spacing(7) 0 govuk-spacing(7) 0;
-  }
-}
-
 // Dropdown menu items.
 .gem-c-layout-super-navigation-header__dropdown-list-item {
   box-sizing: border-box;
@@ -890,25 +869,6 @@ $after-button-padding-left: govuk-spacing(4);
   }
 }
 
-// Popular links.
-.gem-c-layout-super-navigation-header__popular-item {
-  position: relative;
-  padding: govuk-spacing(1) 0;
-}
-
-.gem-c-layout-super-navigation-header__width-container {
-  @include govuk-media-query($until: "desktop") {
-    margin: 0;
-    margin-top: govuk-spacing(6);
-  }
-
-  @include govuk-media-query($from: "desktop") {
-    margin: 0 auto;
-    max-width: 960px;
-    padding: govuk-spacing(5);
-  }
-}
-
 .gem-c-layout-super-navigation-header__column-header {
   font-size: 24px;
 }