[3pt] Remove ambiguous variables from delineate

[CarsonPruitt-NOAA]

I'm totally taking the blame for this one, but we really should make these variable names more descriptive in lines 7 through 12 of delineate_hydros_and_produce_HAND.sh.

b_arg and z_arg should be something more like nwm_subset and nwm_catchments_proj, respectively. Please make sure that these new arg names don't conflict with any exiting ones and replace them throughout this module.