ci(docker): remove database volume

Finally found in Azure the message "Custom storage volume(s) failed to initialize"; this removes the database volume
to see if it resolves the problem.

This does mean there's no mechanism to persist data between deploys, but given it's a development environment that's the
behaviour I'd expect.

Refs #390

deploy/docker-compose-dev.yml

@@ -22,19 +22,13 @@ services:
 
   prereview-db:
     image: postgres:12-alpine
-    volumes:
-      - prereview-db_data:/var/lib/postgresql/data
     networks:
       - prereview-private
     environment:
-      PGDATA: /var/lib/postgresql/data/pgdata
       POSTGRES_USER: prereview
       POSTGRES_PASSWORD: ${PREREVIEW_DB_PASS}
       POSTGRES_DB: prereview
 
-volumes:
-  prereview-db_data: {}
-
 networks:
   prereview-private:
     internal: true