Discovered by @mfilip during testing for PR #1456.

The koji.util.deprecated() function uses Python's warnings module to warn about the deprecation. This module outputs to stderr by default, but under normal circumstances kojid's stderr is not captured. Only messages in the logging system go do kojid.log.

The warning can be seen if kojid is run in the foreground with --fg. Also, technically, systemd runs kojid with --fg, so the output can be seen with journalctl, e.g. journalctl -u kojid -n 10000 |grep -i deprecation.