rustdoc: remove unused CSS color: inherit

This code was added back when `border-color: currentColor` was used.
Since it was changed in ad9a89eef2, the
current color is not used any more.

src/librustdoc/html/static/css/settings.css

@@ -7,7 +7,6 @@
 	margin-right: 0.3em;
 	height: 1.2rem;
 	width: 1.2rem;
-	color: inherit;
 	border: 2px solid var(--settings-input-border-color);
 	outline: none;
 	-webkit-appearance: none;