rustdoc: stop hiding focus outlines on non-rustdoc-toggle details tags

We really shouldn't be overriding this kind of stuff unless the browser
default is really broken (like outlining the thing that isn't clickable).
This directly reverts b8f4e74.

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

@@ -292,10 +292,6 @@ p:last-child {
 	margin: 0;
 }
 
-summary {
-	outline: none;
-}
-
 /* Fix some style changes due to normalize.css 8 */
 
 button {
@@ -1538,6 +1534,8 @@ details.rustdoc-toggle > summary.hideme {
 
 details.rustdoc-toggle > summary {
 	list-style: none;
+	/* focus outline is shown on `::before` instead of this */
+	outline: none;
 }
 details.rustdoc-toggle > summary::-webkit-details-marker,
 details.rustdoc-toggle > summary::marker {