Remove one of duplicated diffpy source code

[bobleesj]

As you've pointed out here #57 (comment), one of the duplicate diffpy folders was removed.

Checklist:

• local Pytest test
• CI test https://github.com/bobleesj/diffpy.snmf/actions/runs/10291369530
• reviewed PR

[bobleesj]

There seems to be a problem with Codecov. I will further investigate this.

src/diffpy/snmf/tests/test_subroutines.py::test_reconstruct_signal[trs2] PASSED [100%]
============================= 104 passed in 5.60s ==============================
No data to report.
Error: Process completed with exit code 1

[bobleesj]

@sbillinge Please review. Fixed the problem. It was the source path within .coveragerc.