Fix the workaround for removing test deprecation warning in PR#170

[bobleesj]

History:

• Tieqiong identified the tests failing in dev mode: https://github.com/diffpy/diffpy.pdfgui/issues/162
• Tieqiong found a workaround with a new merged PR: https://github.com/diffpy/diffpy.pdfgui/pull/170/files

Improvement:

• The merged PR fixes depreciation warning and runs tests.
• It was discussed during a meeting (@sbillinge) that we want to clean up (remove files) and reduce technical debt.

[sbillinge]

I think we just need to bring everything up to cookiecutter standards for running tests here?