Delete user quicktool drop down should have an empty or invalid selection as the default

The revamped user delete quick tool should not default to "Retain posts" in the drop down but something like "Delete user..." or "Please make a selection" there might be an appropriate language string already present for this. I've set this as major as if a user gets confused data loss can occur and the confirmation box doesn't tell you what you're about to do, another bug in itself there!