Replace tasklist-completed workflow with task list checker app

[TeaganKing]

The task list completed workflow doesn't work if a comment is updated but no commit is made. We'd like to use the task list checker app. Joel helped us implement the task list checker app in CUPiD, so I would now like to remove the workflow.

• Have you followed the guidelines in our Contributor's Guide (including the pre-commit check)?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Does your submission pass tests?
• Have you lint your code locally prior to submission?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully tested your changes locally?

[mnlevy1981]

Looks good! Thanks for figuring out how to get a checklist into our workflow :)