Fix build error related to missing header

Currently only the variable "Slicer_Libs_INCLUDE_DIRS" is exposed after
finding Slicer. Ideally, variable like vtkITK_INCLUDE_DIRS should also be
available. It would provide more granularity.
See http://www.na-mic.org/Bug/view.php?id=2882

Specify VTK_LIBRARIES and remove extra libraries.