Drop unused Docker images of dogfooding

.cirrus.yml

@@ -304,26 +304,6 @@ promote_task:
   script:
     - ./private/cirrus/cirrus-promote.sh
 
-dogfood_docker_build_task:
-  name: build docker
-  only_if: $CIRRUS_BRANCH == 'dogfood-on-next'
-  depends_on:
-    - build
-    - validate
-    - promote
-  env:
-    CIRRUS_CLONE_DEPTH: 50
-  gce_instance:
-    image_project: ci-cd-215716
-    image_name: docker-builder-v1
-    zone: us-central1-a
-    disk: 10
-    cpu: 1
-    memory: 1G
-    preemptible: false
-  build_script:
-    - ./private/cirrus/cirrus-build-dogfood-docker.sh
-
 sql_mssql2017_task:
   depends_on: build
   # Comment the following line and commit with message "DO NOT MERGE" in order to run