[FIX] base_location_geonames_import: avoid code duplicates in country states

[Tisho99]

Currently, some countries like Bulgaria, Latvia and Sweden can't be imported with this module due to a duplicity in the code of their states on the data files.

With this fix, the states with the same code of another already parsed are discarded, and countries can be imported in spite of having an error of one of their state codes

T-5767