COMP: Ensure TubeTK CLI build against Slicer register the ITKIO factories

    This commit fixes the problem  avoiding forcing the CLI library wrapper
    variable into the cache.

    Forcing the values into the cache is not needed because

     (1) when TubeTK is built standalone it will use the default wrapper
    provided by the SlicerExecutionModel

    and

     (2) when TubeTk is build against Slicer, the SlicerConfig.cmake will
    set the Slicer SEM wrapper variables in the current scope that
    will then be picked up automatically by the following call to
    find_package(SlicerExecutionModel)

    As detailed in (1), this commit also remove the uneeded tubeTk CLI wrapper.

    Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>
Merge pull request #376 from cdeepakroy/fix-tubetk-build-against-Slicer-cleaned

COMP: Ensure TubeTK CLI build against Slicer register the ITKIO factorie...