Fix: Live preview of languages removes labels from the language panel

MW ULS uses its api to load the localization. Avoid the conflict with
i18n.load method. Directly use the i18n message stores load method

Bug: 61990
Change-Id: I7ea7e7fc31a0831ae2b2c4b4301fbe81109fdf9d

resources/js/ext.uls.i18n.js

@@ -51,7 +51,7 @@
 		if ( i18n.messageStore.messages[locale] ) {
 			return $.Deferred().resolve();
 		}
-		return i18n.load(
+		return i18n.messageStore.load(
 			mw.util.wikiScript( 'api' ) + '?' + $.param( {
 				action: 'ulslocalization',
 				language: locale