Removed calculate_flux_divergence_at_active_cells.
Removed calculate_flux_divergence_at_active_cells.

Removed calculate_flux_divergence_at_active_cells as it is both
deprecated and broken.

amandersillinois/landlab,laijingtao/landlab,Carralex/landlab,RondaStrauch/landlab,laijingtao/landlab,RondaStrauch/landlab,landlab/landlab,decvalts/landlab,csherwood-usgs/landlab,landlab/landlab,csherwood-usgs/landlab,cmshobe/landlab,ManuSchmi88/landlab,RondaStrauch/landlab,cmshobe/landlab,SiccarPoint/landlab,SiccarPoint/landlab,ManuSchmi88/landlab,landlab/landlab,amandersillinois/landlab,Carralex/landlab,Carralex/landlab,decvalts/landlab,ManuSchmi88/landlab,cmshobe/landlab