BUG: remove deprecated DICOM SEG export from Editor

This functionality depended on now deprecated and non-existing functionality in
the Reporting module. The updated version of the Reporting module uses dcmqi,
https://github.com/QIICR/dcmqi, for DICOM SEG conversion, which in turn has an
interface different from what is used in this implementation.

DICOM SEG export will be provided in the updated Reporting extension, which is
reusing Segment Editor components for editing. It is possible that this export
functionality will be available in the main application in the future.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25564 3bd1e089-480b-0410-8dfb-8563597acbee