storage: remove retry around iterator test
storage: remove retry around iterator test

This test should not need to retry, because object listing is strongly
consistent (see https://cloud.google.com/storage/docs/consistency).

We added the retry because it failed sometimes. I have not been able
to reproduce a failure.

Change-Id: Ib93af979ad414677eb1e885afd020eac05a0dc89
Reviewed-on: https://code-review.googlesource.com/13892
Reviewed-by: Ross Light <dfccc06f14414bff5a59be7fc90abf4404b47fc8@google.com>
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Sarah Adams <2b342d1c32491b4e7587e4a0e291a5f0f95d4167@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go