Rollup merge of #101044 - notriddle:notriddle/css-hidden-by, r=jsha

rustdoc: remove unused CSS for `hidden-by-*-hider`

This CSS seems to have become obsolete with the move to `<details>` tags,
and its corresponding JavaScript was removed in aee054d

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

@@ -1573,12 +1573,6 @@ kbd {
 	cursor: default;
 }
 
-.hidden-by-impl-hider,
-.hidden-by-usual-hider {
-	/* important because of conflicting rule for small screens */
-	display: none !important;
-}
-
 #implementations-list > h3 > span.in-band {
 	width: 100%;
 }