AC-9755:Set default collation to utf8mb4 for MySQL

Author: glo17680

lib/internal/Magento/Framework/DB/Adapter/Pdo/Mysql.php

@@ -150,16 +150,6 @@ class Mysql extends \Zend_Db_Adapter_Pdo_Mysql implements AdapterInterface, Rese
      */
     private const COLUMN_TYPE = ['varchar', 'char', 'text', 'mediumtext', 'longtext'];
 
-    /**
-     * const for charset
-     */
-    private const CHARSET = "utf8mb4";
-
-    /**
-     * const for collation
-     */
-    private const COLLATION = "utf8mb4_general_ci";
-
     /**
      * MySQL column - Table DDL type pairs
      *