Convert *.ncl files to *nc files in the test directory t

[mlee03]

Is your feature request related to a problem? Please describe.
There are a lot of ncl files in the test directory. These files are converted tonetcdf(*.nc) files with ncgen for testing.
Because netcdf files occupy less space, it would be preferable to store the test input files as netcdf files instead of converting the ncl files to netcdf files.

Describe the solution you'd like
Replace all ncl files to netcdf files.

Describe alternatives you've considered
Leave the ncl files as they are currently.

Additional context

[ngs333]

@mlee03
@ceblanton
Is there a need for the size reduction, and how much of a benefit do you get. Note that the large files should already be here:
/home/fms/fre-nctools/test-datasets

[ceblanton]

The advantage of the CDL files is that they are text and therefore more amenable to git tracking. But I don't have a strong opinion.