templates/composer: Remove non-existent secret

The secret not existing causes the deployment to fail during a
validation stage.

```
[ERROR] [openshift_base.py:_validate_resources_used_exist] - [Deployment/composer] Secret db does not exist
```

templates/composer.yml

@@ -150,9 +150,6 @@ objects:
         - name: composer-config
           configMap:
             name: composer-config
-        - name: db-secrets
-          secret:
-            secretName: db
         - name: state-directory
           emptyDir: {}
         - name: cache-directory