Remove variable defaults

These are not set whenever a merged compose file is used

docker-compose.yml

@@ -13,10 +13,6 @@ services:
       interval: 5s
       timeout: 10s
       retries: 10
-    environment:
-      POSTGRES_DB: "${POSTGRES_DB:-newsreader}"
-      POSTGRES_USER: "${POSTGRES_USER:-newsreader}"
-      POSTGRES_PASSWORD: "${POSTGRES_PASSWORD:-newsreader}"
     volumes:
       - postgres-data:/var/lib/postgresql/data
 
@@ -65,11 +61,11 @@ services:
     entrypoint: /app/bin/docker-entrypoint.sh
     command: |
       gunicorn
-      --bind 0.0.0.0:${DJANGO_PORT:-8000}
+      --bind 0.0.0.0:8000
       --workers 3
       newsreader.wsgi:application
     healthcheck:
-      test: /usr/bin/curl --fail http://django:${DJANGO_PORT:-8000} || exit 1
+      test: /usr/bin/curl --fail http://django:8000 || exit 1
       interval: 30s
       timeout: 10s
       retries: 10