Automatic merge from submit-queue (batch tested with PRs 58955, 58968, 58971, 58963, 58298). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

remove dead prefix field

The `Prefix` field was never used.