Remove old and unused _route_flow_old from lake_mapper
Remove old and unused _route_flow_old from lake_mapper

Merge pull request #585 from landlab/mcflugen/remove-cruft-lake_mapper
landlab/landlab,amandersillinois/landlab,landlab/landlab,landlab/landlab,cmshobe/landlab,cmshobe/landlab,cmshobe/landlab,amandersillinois/landlab