pgk/fetching: do not log.Printf()

[MMulthaupt]

Go's logging framework is bad: there is no way to differ between log levels, or be able to tell where a log came from. By default we treat logs to the default logger as warnings. However, we just introduced fingerprint logging in pgk/fetching. This specific log line then appears as a warning in the log, when it actually is just info. Potential fixes include:

• Global package-level logger variable (the usual suspect)
• Object-level logger variable (kinda bonkers because you can end up having to provide it very often)
• Some interface that someone made (ugh)
• Some interface that we made (NIH)