Remove border-bottom from most docblocks.

Headings in the top-doc docblock still get a border-bottom due to a rule
that covers all h2, h3, and h4. Method docblocks are generally h5, and
so don't get a border-bottom anymore.

This fixes a problem where a sub-sub-heading within a method would have
a line that went all the way across the page, creating a division that
made that sub-sub-heading look much more important than it really is.

Author: jsha

src/librustdoc/html/static/css/rustdoc.css

@@ -502,10 +502,6 @@ nav.sub {
 	white-space: pre-wrap;
 }
 
-.docblock h1, .docblock h2, .docblock h3, .docblock h4, .docblock h5, .docblock h6 {
-	border-bottom: 1px solid;
-}
-
 .top-doc .docblock h2 { font-size: 1.3em; }
 .top-doc .docblock h3 { font-size: 1.15em; }
 .top-doc .docblock h4,