saslserv/main: fix some things I broke with the authzid stuff

I've no idea why I added it. Nothing needs it and all it does is break
things. I should just revert it for 7.2 I guess.
core: time_ago(): skip seconds for >1w durations

Make the output shorter. Once it reaches months or even years,
one-second precision isn't that useful anymore.
chanserv/flags: clean up do_list()
chanserv/flags: show absolute timestamp as well
core: time_ago(): make output much shorter (1d 2h 3m 4s)