Document removing the testing within mpas_xarray

Unit testing is performed elsewhere instead.

Author: xylar

design_docs/mpas_xarray_class.md

@@ -110,11 +110,15 @@ addressing any requirements.  These include:
        - `_ensure_list`
        - `_get_datetimes`
        - `_remove_repeated_time_index`
+   - I have removed the ability to run `mpas_xarray.py` as a script and the associated
+     tests.  This is on the premise that 1) the test were outdated and would have
+     needed to be updated to work with the current code and 2) unit testing in
+     `test/test_mpas_xarray.py` takes care of this capability in a better way.
    - I have tried to make variable names a bit more verbose in various places
      (e.g. dataset in place of ds).
    - I have tried to improve the docstrings using a syntax that should be useful
      for generating documentation later on.
-   - I have update unit testing to work with the new inerface, notably the 
+   - I have update unit testing to work with the new inerface, notably the
 
 <h2> Implementation: MPAS-Analysis specific functionality should be supported in
 xarray preprossing <br>