MB-7518: Remove ep_db_init stat

This stat no longer makes sense and always returns 0

Change-Id: Id0d52b50f443419416a3cbbb405cfbc13639b09a
Reviewed-on: http://review.couchbase.org/26033
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>