mtr_t::log_write_low(): Replaces mlog_write_initial_log_record_low().

mtr_t::log_file_op(): Replaces fil_op_write_log().

mtr_t::free(): Write MLOG_INIT_FREE_PAGE.

mtr_t::init(): Write MLOG_INIT_FILE_PAGE2.

mtr_t::page_create(): Write record about the partial initialization
of an index page.

mlog_catenate_ulint(), mlog_catenate_string(),
mlog_open(), mlog_close(): Remove.