Avoid use of wfSetupSession()

This global function has been hard deprecated  and is slated for removal in [T249082](https://phabricator.wikimedia.org/T249082)

includes/TweekiTemplate.php

@@ -21,7 +21,7 @@
  * @file
  * @ingroup Skins
  */
-
+use MediaWiki\Session\SessionManager;
 /**
  * QuickTemplate subclass for Vector
  * @ingroup Skins
@@ -946,10 +946,8 @@ class TweekiTemplate extends BaseTemplate {
 	/**
 	 * Render Login-ext
 	 */
-	function renderLoginExt( $skin, $context ) {		
-		if ( session_id() == '' ) {
-			wfSetupSession();
-		}
+	function renderLoginExt( $skin, $context ) {
+		SessionManager::getGlobalSession()->persist();
 
 		//build path for form action
 		$returntotitle = $skin->getSkin()->getTitle();