Removed unused _num_diag_active_links.
Removed unused _num_diag_active_links.

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