Rename generic layer.sql to actual_layer_name .sql (#1034)

Following layers had generic `layer.sql` name.

- `aerodrome_label`
- `aeroway`
- `housenumber`
- `mountain_peak`
- `park`
- `place`
- `poi`
- `transportation`
- `transportation_name`
- `water_name`

This PR renames `layer.sql` to `aerodrome_label.sql`, `aeroway.sql`...

layers/park/park.yaml

@@ -26,7 +26,7 @@ layer:
     query: (SELECT geometry, class, name, name_en, name_de, {name_languages}, rank FROM layer_park(!bbox!, z(!scale_denominator!), !pixel_width!)) AS t
 schema:
   - ./update_park_polygon.sql
-  - ./layer.sql
+  - ./park.sql
 datasources:
   - type: imposm3
     mapping_file: ./mapping.yaml