Remove R/VTK from Travis since it's not being used
Remove R/VTK from Travis since it's not being used

Kitware/tangelohub,Kitware/tangelohub,Kitware/flow,adsorensen/flow,Kitware/flow,Kitware/flow,Kitware/tangelohub,adsorensen/flow,adsorensen/flow,adsorensen/flow,adsorensen/flow,Kitware/flow