remove defunct undocumented .prettyprint class

Created by: cvrebert

Per #10566. /to @mdo

less/code.less

@@ -35,11 +35,6 @@ pre {
   border: 1px solid @pre-border-color;
   border-radius: @border-radius-base;
 
-  // Make prettyprint styles more spaced out for readability
-  &.prettyprint {
-    margin-bottom: @line-height-computed;
-  }
-
   // Account for some code outputs that place code tags in pre tags
   code {
     padding: 0;