Revert "iterator: don't retry if REFUSED"

This reverts commit bc2a2670 (almost).
It would be best to avoid retrying with the same NS and keep trying with
others (if any), but that would require larger changes if it should work
well, so let's err on the side of sending more queries.
5 jobs for refused-retry in 75 minutes and 2 seconds
Status Job ID Name Coverage
  Build
canceled build:linux:amd64 #72891
amd64 linux docker

passed build:linux:amd64 #11994
docker linux amd64

00:00:33

 
  Test
passed deckard:linux:amd64 #11996
docker linux amd64

00:00:31

passed respdiff:linux:amd64 #11997
amd64 docker linux

01:15:02

passed test:linux:amd64 #11995
docker linux amd64

00:00:21