[PATCH] contrib/importers/keepass2csv2pass.py: remove deprecated 'U' open mode

[a87fe1a4-9565-4625-b062-f7e1f655be57]

Having also encountered this issue recently, I was about to submit a patch 
myself until I saw this. I'm bumping this thread so that it has a chance of 
being looked at again and perhaps accepted.