Remove useless override

That method is already defined in the parent interface.

This was shown as an error by Psalm but should not be considered one
IMO. See https://github.com/vimeo/psalm/pull/3203

lib/Doctrine/DBAL/Driver/DriverException.php

@@ -24,13 +24,6 @@ interface DriverException extends Throwable
      */
     public function getErrorCode();
 
-    /**
-     * Returns the driver error message.
-     *
-     * @return string
-     */
-    public function getMessage();
-
     /**
      * Returns the SQLSTATE the driver was in at the time the error occurred.
      *