remove unused columns from word and search_name_* tables

  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