Revert "[TLS-446] Update pipeline to use gpctl" (#160900)

Reverts elastic/kibana#160508 gpctl clones the repo to verify the
commit, but since cloning kibana is not trivial, ill revert for now,
until we find a better way to handle the above on gpctl.

.buildkite/scripts/steps/artifacts/docker_image.sh

@@ -83,18 +83,9 @@ echo "--- Trigger image tag update"
 if [[ "$BUILDKITE_BRANCH" == "$KIBANA_BASE_BRANCH" ]]; then
   cat << EOF | buildkite-agent pipeline upload
 steps:
-  - label: ":argo: Update kibana image tag for kibana-controller using gpctl"
-    async: true
-    branches: main
-    trigger: gpctl-promote
-    build:
-      env:
-        SERVICE_COMMIT_HASH: $GIT_ABBREV_COMMIT
-        REMOTE_SERVICE_CONFIG: https://raw.githubusercontent.com/elastic/serverless-gitops/main/gen/gpctl/kibana/config.yaml
-
   - trigger: serverless-gitops-update-stack-image-tag
     async: true
-    label: ":argo: Update image tag for Kibana using the legacy script (used in QA/Staging)"
+    label: ":argo: Update image tag for Kibana"
     branches: main
     build:
       env: