rustdoc: remove no-op CSS .location:empty { border: none }

This rule was added in 2bb2a29 to remove a
border placed around the location when it's empty. That rule was removed in
6a5f8b1, so this rule does nothing.

Author: notriddle

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

@@ -522,10 +522,6 @@ img {
 	width: 100px;
 }
 
-.location:empty {
-	border: none;
-}
-
 .block ul, .block li {
 	padding: 0;
 	margin: 0;