Not from Postfix, but if you use a new enough syslog daemon you can do it there. For example, in syslog-ng you can create a filter that matches the localhost connections and in your log statement do a conditional that excludes matches for that filter.
For example (off the top of my head check before using):
filter f_mailNoLocalhost { facility(mail) and not match("matching pattern here");};
That said, you'll probably need to know about them sooner or later and not having them will be a detriment. You could also just filter them out when running through whatever parser you are using to parse them - even if it's just your eyes. ;) Also if running a syslog daemon that doesn't have such capabilities you could set up a cron job to clean (via "grep -v pattern") after the log is rotated.
If the connection count is significant enough to be "polluting" the logs it is significant enough to keep since it may affect troubleshooting.