chore: use vanilla python:3.9 image instead of custom metaflow-test image

Metaflow's code packaging bootstraps boto3/requests (and micromamba for
@conda/@pypi) at runtime, so tests don't need a pre-baked image.

- Remove devtools/docker/metaflow-test/Dockerfile
- Remove build-test-image Tilt resource
- Switch all backends to python:3.9 (drop image_pull_policy=Never)
- Remove CI step waiting for the test image to load

Author: Nissan Pow

.github/workflows/ux-tests.yml

@@ -214,11 +214,6 @@ jobs:
         env:
           SERVICES: ${{ matrix.services }}
 
-      - name: Wait for test image to be loaded into minikube
-        if: matrix.backend != 'local' && matrix.backend != 'sfn-batch'
-        run: |
-          tilt wait --for=condition=Ready uiresource/build-test-image --timeout=300s
-
       - name: Save minikube images to cache
         if: steps.image-cache.outputs.cache-hit != 'true'
         run: devtools/ci/save-minikube-images.sh

devtools/Tiltfile

@@ -191,12 +191,3 @@ local_resource(
     labels=["setup"],
 )
 
-# ---------------------------------------------------------------------------
-# Test image
-# ---------------------------------------------------------------------------
-local_resource(
-    name="build-test-image",
-    cmd="minikube image build -t metaflow-test:python3.9 docker/metaflow-test/",
-    deps=["docker/metaflow-test/Dockerfile"],
-    labels=["test"],
-)

devtools/docker/metaflow-test/Dockerfile

@@ -23,37 +23,28 @@ backends:
     enabled: true
 
   # Argo Workflows + Kubernetes (devstack: minikube + argo-workflows)
-  # Uses a pre-baked image with boto3/requests to skip pip install in every pod.
-  # Build it once: docker build -t metaflow-test:python3.9 devtools/docker/metaflow-test/
   - name: argo-kubernetes
     scheduler_type: argo-workflows
     cluster: default
-    decospec: "kubernetes:image=metaflow-test:python3.9,image_pull_policy=Never"
+    decospec: "kubernetes:image=python:3.9"
     enabled: true
 
   # AWS Step Functions Local + Batch/localbatch (devstack: sfn-local + localbatch)
-  # Uses a pre-baked image with boto3/requests to skip pip install in every container.
-  # Build it once: docker build -t metaflow-test:python3.9 devtools/docker/metaflow-test/
   - name: sfn-batch
     scheduler_type: step-functions
     cluster: null
-    decospec: "batch:image=metaflow-test:python3.9"
+    decospec: "batch:image=python:3.9"
     enabled: true
     # xfail: requires core changes from npow/core-deployer-changes (step_functions.py
     # sfn-local compatibility fixes: ResultSelector on Parallel states, no ProcessorConfig
     # on Map states). Remove once that PR is merged into master.
     xfail_reason: "requires npow/core-deployer-changes (sfn-local compatibility fixes in step_functions.py)"
 
   # Apache Airflow + Kubernetes (devstack: minikube + airflow helm chart)
-  # Uses a pre-baked image with boto3/requests to skip pip install in every pod.
-  # Build it once: docker build -t metaflow-test:python3.9 devtools/docker/metaflow-test/
   - name: airflow-kubernetes
     scheduler_type: airflow
     cluster: default
-    # image_pull_policy is not supported by the Airflow deployer; omit it.
-    # The image tag (python3.9) is non-latest so Kubernetes defaults to
-    # IfNotPresent, which works fine since the image is pre-loaded into minikube.
-    decospec: "kubernetes:image=metaflow-test:python3.9"
+    decospec: "kubernetes:image=python:3.9"
     enabled: true
     # xfail: requires AirflowDeployer from npow/core-deployer-changes (__init__.py
     # registration + airflow_deployer.py + airflow_client.py).