♻️(documentation) remove unused environment variables

Yesterday during a deployment, we discovered that these variables are
unused:
POSTGRES_DB
POSTGRES_USER
POSTGRES_PASSWORD

Author: rouja

docs/examples/helm/impress.values.yaml

@@ -46,9 +46,6 @@ backend:
     DB_USER: dinum
     DB_PASSWORD: pass
     DB_PORT: 5432
-    POSTGRES_DB: impress
-    POSTGRES_USER: dinum
-    POSTGRES_PASSWORD: pass
     REDIS_URL: redis://default:pass@redis-master:6379/1
     AWS_S3_ENDPOINT_URL: http://minio.impress.svc.cluster.local:9000
     AWS_S3_ACCESS_KEY_ID: root

docs/installation/kubernetes.md

@@ -168,9 +168,6 @@ DB_NAME: impress
 DB_USER: dinum
 DB_PASSWORD: pass
 DB_PORT: 5432
-POSTGRES_DB: impress
-POSTGRES_USER: dinum
-POSTGRES_PASSWORD: pass
 ```
 
 ### Find s3 bucket connection values

src/helm/env.d/dev/values.impress.yaml.gotmpl

@@ -50,9 +50,6 @@ backend:
     DB_USER: dinum
     DB_PASSWORD: pass
     DB_PORT: 5432
-    POSTGRES_DB: impress
-    POSTGRES_USER: dinum
-    POSTGRES_PASSWORD: pass
     REDIS_URL: redis://default:pass@redis-master:6379/1
     DJANGO_CELERY_BROKER_URL: redis://default:pass@redis-master:6379/1
     AWS_S3_ENDPOINT_URL: http://minio.impress.svc.cluster.local:9000