Revert "Fixes #1856: The default CSS class for hint generated by `ActiveField` is changed to `help-block`"

This reverts commit 7ae4695d0cf46f3347ff8f340f572a08419f21a7.

web/css/site.css

@@ -76,6 +76,12 @@ a.desc:after {
     white-space: nowrap;
 }
 
+.hint-block {
+	display: block;
+	margin-top: 5px;
+	color: #999;
+}
+
 .error-summary {
 	color: #a94442;
 	background: #fdf7f7;