rustdoc: simplify section anchor CSS

Since f50bf86 changed anchors to be
always positioned absolute, specifying it on hover as well is redundant.

Author: notriddle

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

@@ -689,14 +689,10 @@ a {
 	position: relative;
 }
 
-.small-section-header:hover > .anchor {
+.small-section-header:hover > .anchor, .impl:hover > .anchor,
+.trait-impl:hover > .anchor, .variant:hover > .anchor {
 	display: initial;
 }
-
-.impl:hover > .anchor, .trait-impl:hover > .anchor, .variant:hover > .anchor {
-	display: inline-block;
-	position: absolute;
-}
 .anchor {
 	display: none;
 	position: absolute;