Remove unused osm_transportation_merge_linestring table (#1171)

PR #1168 removed several `WHERE` clauses in the `transportation_merge_*` table series.  With those removed, it appears that `osm_transportation_merge_linestring_gen_z8` and `osm_transportation_merge_linestring` are nearly identical, with the former simply adding an `ST_Simplify()` operation.

A grep of the codebase indicates that the _only_ use for `osm_transportation_merge_linestring` is to hold the intermediate result of an `ST_Dump(geometry))` before it is fed into `ST_Simplify()`.  Therefore, it appears that we're holding an entire zoom 8 copy of the transportation layer (all motorway/trunk/primary roads) in a materialized view for absolutely no reason at all.

This PR removes the `osm_transportation_merge_linestring` intermediate table and changes the definition of `osm_transportation_merge_linestring_gen_z8` to perform the `ST_Dump()` and `ST_Simplify()` transformations directly from the `osm_highway_linestring` table in a single operation.

layers/transportation/update_transportation_merge.sql

@@ -102,11 +102,11 @@ WHERE highway NOT IN ('tertiary', 'tertiary_link')
 CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_gen_z9_geometry_idx
     ON osm_transportation_merge_linestring_gen_z9 USING gist (geometry);
 
--- etldoc: osm_highway_linestring ->  osm_transportation_merge_linestring
-DROP MATERIALIZED VIEW IF EXISTS osm_transportation_merge_linestring CASCADE;
-CREATE MATERIALIZED VIEW osm_transportation_merge_linestring AS
+-- etldoc: osm_highway_linestring ->  osm_transportation_merge_linestring_gen_z8
+DROP MATERIALIZED VIEW IF EXISTS osm_transportation_merge_linestring_gen_z8 CASCADE;
+CREATE MATERIALIZED VIEW osm_transportation_merge_linestring_gen_z8 AS
 (
-SELECT (ST_Dump(geometry)).geom AS geometry,
+SELECT ST_Simplify((ST_Dump(geometry)).geom, ZRes(10)) AS geometry,
        NULL::bigint AS osm_id,
        highway,
        network,
@@ -131,25 +131,6 @@ FROM (
          GROUP BY highway, network, construction, is_bridge, is_tunnel, is_ford
      ) AS highway_union
     ) /* DELAY_MATERIALIZED_VIEW_CREATION */;
-CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_geometry_idx
-    ON osm_transportation_merge_linestring USING gist (geometry);
-
--- etldoc: osm_transportation_merge_linestring -> osm_transportation_merge_linestring_gen_z8
-DROP MATERIALIZED VIEW IF EXISTS osm_transportation_merge_linestring_gen_z8 CASCADE;
-CREATE MATERIALIZED VIEW osm_transportation_merge_linestring_gen_z8 AS
-(
-SELECT ST_Simplify(geometry, ZRes(10)) AS geometry,
-       osm_id,
-       highway,
-       network,
-       construction,
-       is_bridge,
-       is_tunnel,
-       is_ford,
-       z_order
-FROM osm_transportation_merge_linestring
-     -- Current view: motorway/trunk/primary
-    ) /* DELAY_MATERIALIZED_VIEW_CREATION */;
 CREATE INDEX IF NOT EXISTS osm_transportation_merge_linestring_gen_z8_geometry_idx
     ON osm_transportation_merge_linestring_gen_z8 USING gist (geometry);
 
@@ -258,7 +239,6 @@ DECLARE
     t TIMESTAMP WITH TIME ZONE := clock_timestamp();
 BEGIN
     RAISE LOG 'Refresh transportation';
-    REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring;
     REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring_gen_z8;
     REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring_gen_z7;
     REFRESH MATERIALIZED VIEW osm_transportation_merge_linestring_gen_z6;