rustdoc: remove no-op mobile CSS .sidebar { margin: 0; padding: 0 }

This isn't overriding anything, because the sidebar never has a margin or
padding on it.

Author: notriddle

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

@@ -1660,8 +1660,6 @@ in storage.js
 		/* Hide the sidebar offscreen while not in use. Doing this instead of display: none means
 		   the sidebar stays visible for screen readers, which is useful for navigation. */
 		left: -1000px;
-		margin: 0;
-		padding: 0;
 		z-index: 11;
 		/* Reduce height slightly to account for mobile topbar. */
 		height: calc(100vh - 45px);