There is only one log_sys and only one log_sys.log.

log_t::files::create(): Replaces log_init().

log_t::files::close(): Replaces log_group_close(), log_group_close_all().

fil_close_log_files(): if (free) log_sys.log_close();
The callers that passed free=true used to call log_group_close_all().

log_header_read(): Replaces log_group_header_read().

log_t::files::file_header_bufs_ptr: Use a single allocation.

log_t::files::file_header_bufs[]: Statically allocate the pointers.

log_t::files::set_fields(): Replaces log_group_set_fields().

log_t::files::calc_lsn_offset(): Replaces log_group_calc_lsn_offset().
Simplify the computation by using fewer variables.

log_t::files::read_log_seg(): Replaces log_group_read_log_seg().

log_sys_t::complete_checkpoint(): Replaces log_io_complete_checkpoint().

fil_aio_wait(): Move the logic from log_io_complete().