[#653] Support removal old combined objects

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

api/data/tree.go

@@ -20,6 +20,12 @@ type NodeVersion struct {
 	IsCombined    bool
 }
 
+// OIDInfo represent OID to delete.
+type OIDInfo struct {
+	ID         oid.ID
+	IsCombined bool
+}
+
 // ExtendedNodeVersion contains additional node info to be able to sort versions by timestamp.
 type ExtendedNodeVersion struct {
 	NodeVersion *NodeVersion