gha: remove reference to vectorized org

This organization has been deprecated for a while now. Based on usage
stats from dockerhub, zero pulls have been performed since july/2024, so
customers/community aren't pulling from this org anymore and thus is
safe to stop publishing to it.

.github/workflows/docker-image.yml

@@ -36,7 +36,6 @@ jobs:
         with:
           # list of Docker images to use as base name for tags
           images: |
-            vectorized/kminion
             redpandadata/kminion
           # generate Docker tags based on the following events/attributes
           # Semver type is only active on 'push tag' events,