How to disable logging to system.log in OS X?
Logging to system.log is controlled by the /etc/asl.conf file.  The default is to send all kernel messages to system.log.  If you add a priority level restriction, the trivial system complaints won't be logged.

Edit the file /etc/asl.conf and find a line that looks like this

? [= Sender kernel] file system.log


and change it to 

? [= Sender kernel] [&lt;= Level error] file system.log


Send a HUP signal to the syslogd process (or just restart your system) and the logging behavior will be changed.  Use pgrep from Terminal to find the process ID for syslogd.  E.g.

$ pgrep syslogd
21
$


Then send a HUP signal to that process ID with the kill program.

$ sudo kill -HUP 21
$