stop checking for physical vbucket presense in compaction daemon

Because there's no need.

Change-Id: I01ca83ced22eeae0252affec9a505427d1b9a948
Reviewed-on: http://review.couchbase.org/35930
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>