Can I remove LM log file

You can't remove it. At least, if you do, it'll just get regenerated the next time the process has something to log. 

You can decrease logging if that's your goal. On the Collectors page, click the logs icon on the Collector you want to modify. Click the Manage button that appears. You can change the log level for the various components up or down. You can move it all the way to "disable" if you want to. Please consider reaching out to support when doing this as not having log information will cause issues when Support needs to help you with troubleshooting.