STYLE: Do not explicitly import "freesurfer" into "slicer" module

FreeSurfer classes are expected to be used by explicitly importing the
module.

The classes are not used in either Slicer core or any of the extensions
available in the extensions index.

Slicer core:

$ for class in $(ls -1 ./Libs/FreeSurfer/vtk*.h | cut -d"/" -f4 | cut -d"." -f1); do echo "Looking for $class [$(pwd)]"; ack --py $class; done
Looking for vtkFreeSurferWin32Header [/home/jcfr/Projects/Slicer]
Looking for vtkFSIO [/home/jcfr/Projects/Slicer]
Looking for vtkFSLookupTable [/home/jcfr/Projects/Slicer]
Looking for vtkFSSurfaceAnnotationReader [/home/jcfr/Projects/Slicer]
Looking for vtkFSSurfaceHelper [/home/jcfr/Projects/Slicer]
Looking for vtkFSSurfaceLabelReader [/home/jcfr/Projects/Slicer]
Looking for vtkFSSurfaceReader [/home/jcfr/Projects/Slicer]
Looking for vtkFSSurfaceScalarReader [/home/jcfr/Projects/Slicer]
Looking for vtkFSSurfaceWFileReader [/home/jcfr/Projects/Slicer]

Extensions:

$ for class in $(cd /home/kitware/Dashboards/Nightly/Slicer-0; ls -1 ./Libs/FreeSurfer/vtk*.h | cut -d"/" -f4 | cut -d"." -f1); do echo "Looking for $class [$(pwd)]"; ack-grep --py $class; done
Looking for vtkFreeSurferWin32Header [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSIO [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSLookupTable [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSSurfaceAnnotationReader [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSSurfaceHelper [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSSurfaceLabelReader [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSSurfaceReader [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSSurfaceScalarReader [/home/kitware/Dashboards/Nightly/S-0-E-b]
Looking for vtkFSSurfaceWFileReader [/home/kitware/Dashboards/Nightly/S-0-E-b]

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25127 3bd1e089-480b-0410-8dfb-8563597acbee