Remove unused CSS. (#24872)

Author: XhmikosR

assets/scss/_featured-sites.scss

@@ -41,11 +41,6 @@
   }
 }
 
-.bd-pretext {
-  overflow: hidden;
-  resize: none;
-}
-
 .half-rule {
   width: 6rem;
   margin: 2.5rem 0;

assets/scss/_masthead.scss

@@ -32,15 +32,12 @@
 @import "variables";
 @import "nav";
 @import "masthead";
-@import "featured-sites";
 @import "ads";
 @import "content";
-@import "page-header";
 @import "skiplink";
 @import "sidebar";
 @import "footer";
 @import "component-examples";
-@import "responsive-tests";
 @import "buttons";
 @import "callouts";
 @import "examples";