MB-9058: Remove all references to the database files

Access to the database files is no longer needed as
the information now gets in through the UPR stream.

A check for purging was removed. That is OK since with
UPR the logic to deal with purges needs to be re-done
anyway.

Change-Id: I3b751905867cda4453ebd98cbf48bd8144fbae0b
Reviewed-on: http://review.couchbase.org/29405
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>