`start_log.log` gets all info level logs

`start_log.log` is used to write the log messages that we are producing before our logging to graylog is initialised. Once we're putting logs into graylog we shouldn't need to put anything in `start_log.log`. However, we still are. This will hog disk space if left long enough. Current;ly, given https://github.com/DiamondLightSource/mx-bluesky/issues/257 this is not much of an issue, but it may become one if that is fixed