Do what we can to ensure that old log files are deleted

We should encourage people, especially relay operators and onion service operators, to store their logs in such a way as to ensure that they can get deleted after a while, rather than kept forever.

For tracing_appender file logs, this might involve manual deletion, or upstreaming a patch to delete old logs.

For journald logs, this will involve a big old kludge, if it's possible at all.