fix(e2e): remove obsolete version tag in docker compose files leading to warning

Author: taepper

docker-compose-for-tests-api.yml

@@ -1,4 +1,3 @@
-version: "3.9"
 services:
   silo:
     image: ${SILO_IMAGE}

docker-compose-for-tests-preprocessing-from-ndjson.yml

@@ -1,4 +1,3 @@
-version: "3.9"
 services:
   silo:
     image: ${SILO_IMAGE}