OSBA: Use public image

[krancour]

Now that we've opened up the microsoft/azure-service-broker (name will change at some point in the near future to match open-service-broker-azure), we no longer need to pull private images from quay.io/deis/azure-service-broker using an ImagePullSecret.

The default image in values.yaml should be updated and templates/deis-pull-secret.yaml should be removed.