The .<number> logs are temporary and should be merged with the main log (#channel.ircNetwork.log)
If you want, you can check the temporary logs to see if they have been merged in the main log or not. If they have, then you can safely delete them.
The fact that they aren't being deleted automatically has been mentioned before, but, to my knowledge, there hasn't been a repeatable method of determining when they are or are not deleted.
In theory, I believe, they should be merged with the main log file when you leave a channel (whether by parting, quitting, or being kicked).
