Remove deprecated auth from GlanceImageService
Remove deprecated auth from GlanceImageService

* Drop the code block specific to deprecated auth in image
  deletion code
* Remove reference to deprecated auth in the auth_strategy
  config option help text
* Related to bp remove-deprecated-auth

Change-Id: Id0f4f287d33d01d54642fbc544ada9b7ef1b83ec

n0ano/gantt,n0ano/gantt