The `recorder.PastEventf` method wasn't actually working as advertised.
It was supposed to accept a timestamp, which would be used when
generating the event. However, as the
[source code](https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/client-go/tools/record/event.go#L316)
shows, this `timestamp` was never actually used.
In other words, `PastEventf` is identical to `Eventf`.
We have two options: one would be to fix `PastEventf` so that it works
as advertised. The other would be to delete `PastEventf` and only
support `Eventf`.
Ultimately, I could only find one use of `PastEventf` in the code base,
so I propose we just delete `PastEventf` and convert all uses to
`Eventf`.
