Remove netCDF test and init files

[timspainNERSC]

The netCDF files that are currently included in the repo take a lot of the limited storage space. Many of them are generated from python script and could be recreated as part of the build process, thereby saving the storage space.

[timspainNERSC]

All of the .nc files are generated from included python scripts and simple data sources, with the exception of init_25km_NH.nc, which requires the sizeable TOPAZ4 data files to be generated.