* Added method to set xy coords without loops. Removed unused attributes.
* Added method to set xy coords without loops. Removed unused attributes.

Added
=====

* Use sgrid.node_coords to set node x, y coordinates without loops.

Removed
=======

* Removed unused attribute _node_z. A RasterModelGrid is only 2D, so the
  _node_z array wasn't used.
* Removed get_node_z_coords method function.



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