Delete registry secret code from oadp-operator - OADP 1.2

[weshayutin]

For OADP 1.1+ Currently we reconcile secrets for registry environment variables inside oadp-operator repo.

openshift-velero-plugin then from BSL name, refer back to a hardcoded pattern for a secret name that registry retrieves environment variables from.

Removing this reduce complexity in debugging/updating the "plugin registry" component going forward.