rustdoc: remove no-op CSS .scrape-help { background: transparent }

It's a link. This is the default CSS for it.

Author: notriddle

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

@@ -1984,7 +1984,6 @@ in storage.js
 	font-size: 12px;
 	position: relative;
 	bottom: 1px;
-	background: transparent;
 	border-width: 1px;
 	border-style: solid;
 	border-radius: 50px;