Cleanup: remove generation of tarantool_box_cfg.cfg

Remove auto-generation of tarantool_box_cfg.cfg.
This was intended as a sample configuration
file, but it is no longer syntactically correct,
and thus can not be used.
Besides, there are now semantical rules on top
of the syntax restrictions (e.g. you can't define
memcached_expire on a replica), which also
make the auto-generated config incorrect.

Remove it to not mislead first-time users into
trying it out.