Fix enumeration in SBS1 list pruning.

python/sbs1.py

@@ -83,7 +83,7 @@ class output_sbs1:
     # dictionary is getting too large.
     if len(self._aircraft_id_map) > 1e4:
       minimum = min(self._aircraft_id_map.values()) + (len(self._aircraft_id_map) - 1e4)
-      for icao, _id in self._aircraft_id_map:
+      for icao, _id in self._aircraft_id_map.iteritems():
         if _id < minimum:
             del self._aircraft_id_map[icao]