As per the revised SRBAC community goals, glance service is now
switching to new defaults by default hence removing the deprecated
``enforce_secure_rbac`` option which is no longer needed.
The ``enforce_secure_rbac`` option was introduced EXPERIMENTAL in
Wallaby release for operators to opt into enforcing authorization
based on common RBAC personas.
Related blueprint secure-rbac
Change-Id: I273527c85d30c1c09c086c73c892aaa6d127df6b
b20cc91e6f