chore: replace deprecated function calls

[ycexiao]

Problem

Running pytest will get:

=================================================== warnings summary ===================================================
tests/test_pdfadapter.py::test_pdfadapter
tests/test_runmacro.py::test_meta_model
  /Users/yuchen/Projects/diffpy/diffpy.apps/tests/helper.py:40: DeprecationWarning: 'diffpy.structure.getParser' is deprecated and will be removed in version 4.0.0. Please use 'diffpy.structure.get_parser' instead.
    p_cif = getParser("cif")
...

Some warnings are from diffpy.apps itself, but some are from it's dependencies.

Proposed solution

Replace the deprecated function calls