BUG: Revert "ENH: add support of DCMTK private dictionary"

This reverts commit 1c20e6fc3adad65c72bc3bc3091e636b5e7080c0.

For unknown reason, this commit appears to break the dashboard.
The messages reported on dashboard are contradicting, since config
and build errors are reported on the front page, but not for the Slicer4
project, see

http://slicer.cdash.org/index.php?project=Slicer4&date=2015-07-01

Experiments trying to package Slicer on mac failed, with or without this
commit, as documented in

https://github.com/Slicer/Slicer/pull/299

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24368 3bd1e089-480b-0410-8dfb-8563597acbee