Bug-fix for WRF model_mod nc_write_model_atts
Removes obsolete domain dimension from nc_write_model_atts for WRF model_mod.
This code was left over from when multiple domains could be written to a single NetCDF file in DART.
No changes to assimilation results, but the following WRF variables will written as single values:
DY, TRUELAT1, TRUELAT2, STAND_LON, CEN_LAT, CEN_LON, MAP_PROJ, PERIODIC_X, POLAR