trx_rseg_mem_restore(): Update the max_trx_id from the undo log pages.

trx_sys_init_at_db_start(): Remove; merge with trx_lists_init_at_db_start().

trx_undo_lists_init(): Move to the only calling module, trx0rseg.cc.

trx_undo_mem_create_at_db_start(): Declare globally. Return the number
of pages.