WL#10499: InnoDB: Change Default for innodb_undo_log_truncate from OFF to ON

As a result of WL#10498 we should change the default value for
innodb_undo_log_truncate from OFF to ON.

WL#10498 changed the default value for innodb_undo_tablespaces to 2 so that by
default, there will be at least 2 undo tablespaces for InnoDB to truncate.  Even
if innodb_undo_tablespace is explicitly set to 0, this setting will not cause a
problem.  The purge thread will spend a small amount of time looking for an
independent undo tablespace to truncate and not find any.

FR1: The default value for innodb_undo_log_truncate is seen as ON.

Change the default value for innodb_undo_log_truncate from OFF to ON.