Let callers specify which storage to operate on.

Since CE and DE storage can have different availability lifecycles,
callers can't operate on both at the same time.  Let them use flags
to specify which storage to work with.

Remove old unused methods, and name consistently in preparation for
eventual move to AIDL.

Bug: 26466827
Change-Id: Id5d7d03f5d8814864eea801f5a46496c085afdff