recv_sys_t opened redo log files along with log_sys_t. That's why I
removed file sharing logic from InnoDB
in 9ef2d29f
But it was actually used to ensure that only one MariaDB instance
will touch the same InnoDB files.

os0file.cc: revert some changes done previously

mapped_file_t::map(): now has arguments read_only, nvme

file_io::open(): now has argument read_only

class file_os_io: make final

log_file_t::open(): now has argument read_only