Remove index on name_vector. We always do near search where the
geometry index is sufficient. Also split centroid index in low
and high rank indexes. Reduces index size by about 25%.
The country information can be determined sufficiently from
the country code. We only loose the specific OSM object
behind the address.
Also streamlines the location_area_country table.
Removes 'trigram' and 'location' from word.
Removes 'address', 'importance' and 'country_code' from search_name_*.
Use full geometry in centroid column of search_name_*.
Requires migration of existing tables. For more info see pull request
https://github.com/twain47/Nominatim/pull/45