docs(pubsub): Fix documentation for PubSub.configure
docs(pubsub): Fix documentation for PubSub.configure

* Remove retries property that does not exist in code.

closes: #14410
pr: #14432
googleapis/google-cloud-ruby,dazuma/google-cloud-ruby,googleapis/google-cloud-ruby,googleapis/google-cloud-ruby,dazuma/google-cloud-ruby,googleapis/google-cloud-ruby,dazuma/google-cloud-ruby,dazuma/google-cloud-ruby,googleapis/google-cloud-ruby,dazuma/google-cloud-ruby,googleapis/google-cloud-ruby,dazuma/google-cloud-ruby