Replace verbose event processing logging

[tnull]

In #3314 we introduced logging around event processing.

Logging in the event processing loop will however turn out to be very spammy, in particular since we recently introduced fallible event handling in which case we directly loop around and retry processing.

We should move the logging to calling handle_event (see #3314 (comment)) but probably want to introduce some kind of delay before retrying event handling (which we discussed before, but didn't actually do in #2995.