[#1559] metabase: Remove public functions

Reduce public interface of this package. Later each result will contain
an additional status, so it makes more sense to use the same functions
and result processing everywhere.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/local_object_storage/shard/exists.go

@@ -38,7 +38,11 @@ func (p ExistsRes) Exists() bool {
 //
 // Returns an error of type apistatus.ObjectAlreadyRemoved if object has been marked as removed.
 func (s *Shard) Exists(prm ExistsPrm) (ExistsRes, error) {
-	exists, err := meta.Exists(s.metaBase, prm.addr)
+	var existsPrm meta.ExistsPrm
+	existsPrm.WithAddress(prm.addr)
+
+	res, err := s.metaBase.Exists(existsPrm)
+	exists := res.Exists()
 	if err != nil {
 		// If the shard is in degraded mode, try to consult blobstor directly.
 		// Otherwise, just return an error.