db: adjust sstable load to use sstable self-reporting of shard ownership
db: adjust sstable load to use sstable self-reporting of shard ownership

Instead of calculating the owning shard from the sstable's partition
key range, delegate to the new sstable method for getting owning shard
infomation.  This insulates us from changes in the sharding algorithm.

duarten/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,avikivity/scylla,raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,avikivity/scylla,avikivity/scylla