* as_admin param is no longer needed as get_usr_preference()
fetches actually set preference for a susbcriber and used
only by the code (not exposed directly to 'subscriber',
'subscriberadmin' roles
* with the aforedescribed, get_usr_preference() no longer
filters by expose_to_customer, expose_to_subscriber for
'subscriber' and 'subscriberadmin' roles
* refactor get_usr_preferences() to be simple and in line
with the other get_*_preferences() as it's mainly responsible
for fetching the preference as requested by the internal
code
Change-Id: Ia52d8f4ebfd854901bf446e29fb475dea1fba866