ENH: In ITK 4.6, ImageIO GE5 is now registered by default.

No need to manually register the GE5 ImageIO because as of ITK 4.6 it
is registered by default with ITK.

Let's note the GE IO module is enabled by default and there is not need
to explicitly enable it when configuring ITK.

See InsightSoftwareConsortium/ITK@80cacdc

Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

From: Bradley Lowekamp <blowekamp@mail.nih.gov>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23662 3bd1e089-480b-0410-8dfb-8563597acbee