busybox: fix syslog related meta data

busybox: fix syslog related meta data

Set RCONFLICTS to disallow multiple syslog daemon providers to be installed
on the target at the same time,  and remove codes which dealt with such
situation.

Supporting multiple syslog daemons on the same image doesn't have much sense.
rsyslog and syslog-ng in meta-oe have set RCONFLICTS to disallow this. And
we do the same for busybox.

Also, remove the line of creating a meaningless symlink of
/lib/systemd/syslog.service to /dev/null.

(From OE-Core rev: 597bbf99ee8e88294f2ed96c84a51f9ed83e8933)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>