api.jquery.com: Fixup a4e2aaa list-item bullets

Follows-up a4e2aaa which converted our custom list-item image
to native CSS `::marker`. However, I didn't realize that
`list-item: none` has no effect on ::marker. You have to set this to
`content: ""` to clear.

themes/jquery/css/base.css

@@ -2543,6 +2543,10 @@ footer .books li a cite {
 	text-shadow: 0 1px 0 #fff;
 }
 
+#content .signatures li::marker {
+	content: "";
+}
+
 #content .signatures li {
 	list-style: none;
 	background: none;