Remove setting permissions for the admin_dashboard.
Remove setting permissions for the admin_dashboard.

There has been a bugfix backported to stable mitaka. The admin
dashboard policy now includes checking the admin role against
the other policy.json files. So we don't need to override the
admin permissions but manage the roles in the policy.json files.

The bug fix commit:
https://github.com/openstack/horizon/commit/0a8b2062dbde7f1a69a5f6cff52fb4f6a6effe61

blueboxgroup/horizon-customization