NOOP water - Move updating sql into separate file (#920)

Use `update_water.sql` for all queries that update db
to be consistent with the other layers.

layers/water/water.yaml

@@ -34,6 +34,7 @@ layer:
   datasource:
     query: (SELECT geometry, class, intermittent, brunnel FROM layer_water(!bbox!, z(!scale_denominator!))) AS t
 schema:
+  - ./update_water.sql
   - ./water.sql
 datasources:
   - type: imposm3