Remove no longer necessary row classes

These element had no columns inside and the row classes had only been
added to give them a maximum width. That's no longer necessary since now
the body has that maximum width.

app/assets/stylesheets/layout.scss

@@ -695,12 +695,23 @@ body > header,
 .subnavigation {
   @include full-width-background;
 
+  @include breakpoint(small only) {
+    @include grid-row-nest;
+  }
+
   @include breakpoint(medium) {
     background: $body-background;
     color: $text;
     padding-bottom: 0;
   }
 
+  .search-form-header {
+
+    @include breakpoint(small only) {
+      padding-left: rem-calc(map-get($grid-column-gutter, small) / 2);
+    }
+  }
+
   ul {
     list-style-type: none;
     margin: 0;