rustdoc: remove pointless CSS .rightside { padding-right: 2px }

This CSS was added in 34bd2b8, as
`.since { padding-right: 2px }`, to prevent it from uncomfortably touching
the srclink, which was a separate floated element. It was carried forward
with 962c0a4 to the new `.rightside`, but
its role was replaced with adding " • " between them. All it does now
is pushes the element 2px away from the page's right margin.

Removing this rule changes the page layout, but you have to look for it to
notice it.

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

@@ -1051,7 +1051,6 @@ so that we can apply CSS-filters to change the arrow color in themes */
 
 .rightside {
 	padding-left: 12px;
-	padding-right: 2px;
 	float: right;
 }