dtcs: make code to extract non expired tables faster
dtcs: make code to extract non expired tables faster

since it's O(n) and not O(n log n).

change also needed for change in interface of function to retrieve
fully expired tables, or sort lambda would need to be parametrized.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

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