stop making it possible to set ENABLED_LANGUAGES beyond the hardcoded… (#33567)

docker-compose.prod.tmpl.yaml

@@ -14,7 +14,6 @@ services:
       HYDRO_SECRET: ${HYDRO_SECRET}
       HAYSTACK_URL: ${HAYSTACK_URL}
       HEROKU_APP_NAME: ${HEROKU_APP_NAME}
-      ENABLED_LANGUAGES: ${ENABLED_LANGUAGES}
       DEPLOYMENT_ENV: ${DEPLOYMENT_ENV}
       HEROKU_PRODUCTION_APP: true
       PORT: 4000