Revert "Use Codex styles for buttons in language overlay"

This reverts commit d29050d080.

Reason for revert: I had mistakenly assumed the @wikimedia/codex
module was loaded on clicking the language button. It appears to
be added on page load.

Given T248718 it's still unclear what our policy on loading
@wikimedia/codex on page load is and given several people are out
I think it would be better to attempt this again next week, possibly
delaying further if needed.

Bug: T353071
Bug: T248718
Change-Id: I09334a1faec06a7400e61013ddda374156bf5d72

resources/js/ext.uls.setlang.js

@@ -42,11 +42,11 @@
 
 	function getButtons() {
 		$cancelBtn = $( '<button>' )
-			.addClass( 'cdx-button uls-setlang-cancel' )
+			.addClass( 'mw-ui-button uls-setlang-cancel' )
 			.text( mw.msg( 'ext-uls-setlang-cancel' ) );
 
 		$acceptBtn = $( '<button>' )
-			.addClass( 'cdx-button cdx-button--action-progressive active uls-setlang-apply' )
+			.addClass( 'mw-ui-button mw-ui-progressive active uls-setlang-apply' )
 			.text( mw.msg( 'ext-uls-setlang-accept' ) );
 
 		return $( '<div>' )