`ShenandoahVerifier::verify_during_evacuation` is a relaxed version of `ShenandoahVerifier::verify_before_evacuation`. In current code, "during" verification is called shortly after "before" check, which really gains us nothing checking-wise, and only really wastes verification time. This is the only "during" verification check we have, all other checks verify things before/after the phases. It makes sense to remove "during evac" verification check for extra debug performance and cleanliness.