TagLogFormatter: For log entries changing both revid and logid tags, prefer revid

TagLogFormatter: For log entries changing both revid and logid tags, prefer revid

After 68cc94540d1d6f84b267ab742ce8ff3a46e3ec2f, it's possible for a
single user action to add/remove tags to both a log entry and an
associated page revision (for example for file uploads). I think we
should consider the revision to be the "primary" source of information.

(Even better, we could display both. But that seems like a bit more
work and I'm not sure if it'd be helpful.)

Change-Id: I3c1770346bc559b96c39d0ec40b2375954681d15