I ran into the same issue and followed Neil P's suggestion and looked at creating a post deployment script to remove the items. I was already using CI based on the arm template, so this extended my original CI.
As of this writing, Microsoft's power-shell script does work correctly for ADF V2.
Honestly, the approach right now is a little convoluted. I had to set up two branch artifacts. One looks at adf_publish and one that looks at master. adf_publish triggers the release pipeline, master handles the powershell script.
Then, I created a deployment powershell script in my repo on the master branch
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After that, I updated the release pipeline to include the powershell script after the resource was updated. Note that I had to reference the ARMTemplateForFactory.json directly to get the script to work.
Everything worked as expected and the downstream QA release has updated properly and removed obsolete pipelines, etc.