Fix deletion script (#1357)

Because the slice has not done deep clone. All the _Data_ in
_deleteInfo_ will eventually refer to the last item in partition.

Please refer to "reuse slice session" from:
https://pkg.go.dev/github.com/gocql/gocql#hdr-Reusing_slices

tools/cassandra_delete_range/main.go

@@ -484,8 +484,6 @@ func prepareDeleteQueries(cluster *gocql.ClusterConfig, fromLedgerIdx uint64, qu
 
 					var pageState []byte
 					var rowsRetrieved uint64
-					var key []byte
-					var seq uint64
 
 					for {
 						iter := preparedQuery.PageSize(*clusterPageSize).PageState(pageState).Iter()
@@ -493,6 +491,9 @@ func prepareDeleteQueries(cluster *gocql.ClusterConfig, fromLedgerIdx uint64, qu
 						scanner := iter.Scanner()
 
 						for scanner.Next() {
+							var key []byte
+							var seq uint64
+
 							err = scanner.Scan(&key, &seq)
 							if err == nil {
 								rowsRetrieved++