sstables::shared_index_list: use utils::loading_shared_values
sstables::shared_index_list: use utils::loading_shared_values

Since utils::loading_shared_values API is based on the original shared_index_list
this change is mostly a drop-in replacement of the corresponding parts.

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>

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