STYLE: ITK_EXPORT had no use

The defintion of ITK_EXPORT was empty in all cases

This has been identified since 2003 as not being necessary
for builds. see https://issues.itk.org/jira/browse/ITK-3110

On Windows builds that need exports, they must
be unique per library, and that is not controlled by CMake now.

The PrintSelfCheck.tcl was the only remenant need for
This patch, and that is no longer being used, so that
file as been removed.

The ITK_EXPORT define was set to nothing and had no
known remaining purpose.  It was removed to make the
over all code easier to understand.  There was,
understandably, a bit of confusion about the
need for this being pervasive in the code.

It is currently backwards compatible to have
this in code, but at some future point it will
be removed.