remove support for deprecated gazetteer osm2pgsql output

docs/develop/Database-Layout.md

@@ -3,8 +3,7 @@
 ### Import tables
 
 OSM data is initially imported using [osm2pgsql](https://osm2pgsql.org).
-Nominatim uses its own data output style 'gazetteer', which differs from the
-output style created for map rendering.
+Nominatim uses a custom flex style to create the initial import tables.
 
 The import process creates the following tables:
 
@@ -14,7 +13,7 @@ The `planet_osm_*` tables are the usual backing tables for OSM data. Note
 that Nominatim uses them to look up special relations and to find nodes on
 ways.
 
-The gazetteer style produces a single table `place` as output with the following
+The osm2pgsql import produces a single table `place` as output with the following
 columns:
 
  * `osm_type` - kind of OSM object (**N** - node, **W** - way, **R** - relation)

docs/develop/overview.md

@@ -9,7 +9,7 @@ the address computation and the search frontend.
 The __data import__ stage reads the raw OSM data and extracts all information
 that is useful for geocoding. This part is done by osm2pgsql, the same tool
 that can also be used to import a rendering database. It uses the special
-gazetteer output plugin in `osm2pgsql/src/output-gazetter.[ch]pp`. The result of
+flex output style defined in the directory `/lib-lua`. The result of
 the import can be found in the database table `place`.
 
 The __address computation__ or __indexing__ stage takes the data from `place`