Fix bad match with database

Old code was mixes with new code. Don't get the database
from the record, but open it.

Change-Id: I0b376ad71d201754fa3d100c7851a32a2f5f8ffd
Reviewed-on: http://review.couchbase.org/12351
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>

src/geocouch/couch_spatial_compactor.erl

@@ -55,7 +55,6 @@ compact_group(Group, EmptyGroup, DbName) ->
     } = Group,
 
     #spatial_group{
-        db = Db,
         id_btree = EmptyIdBtree,
         indexes = EmptyIndexes,
         fd = EmptyFd