[ticket/12352] Mark salted md5 and phpass passwords driver as legacy

PHPBB3-12352

phpBB/phpbb/passwords/driver/salted_md5.php

@@ -53,6 +53,14 @@ class salted_md5 extends base
 		return self::PREFIX;
 	}
 
+	/**
+	* @inheritdoc
+	*/
+	public function is_legacy()
+	{
+		return true;
+	}
+
 	/**
 	* @inheritdoc
 	*/