Rollup merge of rust-lang#101298 - notriddle:notriddle/rustdoc-main-since, r=GuillaumeGomez

rustdoc: remove unused CSS `#main-content > .since`

This rule was added (actually, it was called `#main > .since` back then) with cdca084 and you can see an example of the bug it's intended to fix in <https://doc.rust-lang.org/1.9.0/std/fmt/fn.write.html> by looking at the `1.0.0` version marker.

However, a5a2f2b changed it so that `<span class="since">` is always placed in an out-of-band wrapper, so it's never nested directly below `#main` / `#main-content` any more.

Author: GuillaumeGomez

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

@@ -215,7 +215,6 @@ details.rustdoc-toggle > summary::before,
 div.impl-items > div:not(.docblock):not(.item-info),
 .content ul.crate a.crate,
 a.srclink,
-#main-content > .since,
 #help-button > button,
 details.rustdoc-toggle.top-doc > summary,
 details.rustdoc-toggle.top-doc > summary::before,