locator: topology: drop unused calculate_datacenters

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

Closes scylladb/scylladb#23647

locator/topology.hh

@@ -427,11 +427,8 @@ private:
 
     bool _sort_by_proximity = true;
 
-    // pre-calculated
     std::unordered_set<sstring> _datacenters;
 
-    void calculate_datacenters();
-
     mutable random_engine_type _random_engine;
 
     friend class token_metadata_impl;