Remove obsolete DOCKERHUB_IMAGE_NAME workaround from CI

The workaround is no longer needed as the functionality is now properly handled by hive/scripts/ci-helpers/build_and_publish_instance.sh (added in hive commit 0428ff61c). MR 565 has been merged, making this TODO redundant.

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>