Fix a bogus UNIV_SYNC_DEBUG failure in the fix of Bug #59641 or Oracle Bug #11766513.
Fix a bogus UNIV_SYNC_DEBUG failure in the fix of Bug #59641
or Oracle Bug #11766513.

trx_undo_free_prepared(): Do not acquire or release trx->rseg->mutex.
This code is invoked in the single-threaded part of shutdown, therefore
a mutex is not needed.
flynn1973/mariadb-aix,flynn1973/mariadb-aix,flynn1973/mariadb-aix,davidl-zend/zenddbi,davidl-zend/zenddbi,davidl-zend/zenddbi,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,slanterns/server,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,ollie314/server,ollie314/server,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,ollie314/server,natsys/mariadb_10.2,davidl-zend/zenddbi,natsys/mariadb_10.2,davidl-zend/zenddbi,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,davidl-zend/zenddbi,davidl-zend/zenddbi,davidl-zend/zenddbi,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2