This is a follow-up fix to the changes that were made in MDEV-7962.

assert_trx_is_free(): Assert !is_wsrep().

trx_init(): Do not initialize trx->wsrep, because it must have been
initialized already.

trx_t::commit_in_memory(): Invoke wsrep_commit_ordered(). This call
was being skipped, because the transaction object had already been
freed to the pool.

trx_rollback_for_mysql(), innobase_commit_low(),
innobase_close_connection(): Always reset trx->wsrep.