Event builder logs growing in size

[Jelle Aalbers]

For current runs the event builder log file is about 75 MB in size. It looks like this is all due to junk at the start.

Perhaps the file-clearing logic at https://github.com/XENON1T/pax/blob/master/bin/event-builder#L295 is problematic. It's still the canonical answer on stackoverflow though... (https://stackoverflow.com/questions/4914277/how-to-empty-a-file-using-python)