rustdoc: remove redundant rule #settings .setting-line

Since the current version of settings.js always nests things below
a div with ID `settings`, this rule always overrode the one above.

Author: notriddle

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

@@ -1,5 +1,5 @@
 .setting-line {
-	margin: 0.6em 0 0.6em 0.3em;
+	margin: 1.2em 0.6em;
 	position: relative;
 }
 
@@ -55,10 +55,6 @@
 	cursor: pointer;
 }
 
-#settings .setting-line {
-	margin: 1.2em 0.6em;
-}
-
 .setting-line .radio-line input:checked {
 	box-shadow: inset 0 0 0 3px var(--main-background-color);
 	background-color: var(--settings-input-color);