Drop the main table for layer `transportation_name` layer before creation.
For the first SQL import, it is OK, but for the second import (e.g. for a different country by `import-osm area=yyy`) without dropping the whole database it will keep `osm_transportation_name_network` filled with data from the first import (after first `import-sql` step)
This PR will drop the already-filled table from the first import and insert data from the reimported area.
382b12ae8a