Double check that the product is completely deleted in Etsy, and doesn't appear in other listing folders (e.g. Drafts, Expired, Sold Out). If not, these products will still appear in Printful.
Go to your Dashboard > Stores > Sync and click Refresh data. This will completely re-sync all your products and start processing the deleted ones. It can take 1-2 hours for Etsy items to disappear from Printful after deletion.