This throwback from the 60s is an absolute nightmare. When I bought my house it had these things in every room of the house and I tried every method imaginable to remove them. The best I could come up with was to just scrape them off and then remove the adhesive by a combination of scraping and sanding. Even then, I finished up having to have a couple of my ceilings re-skimmed to cover the damage caused by the removal process. This said, steam strippers weren't available at the time so I didn't try this method, perhaps that might be worth a go!