Drop CCDBDownloader.h from the CCDB dictionary

The header has no ClassDef and is included only by CCDBDownloader.cxx,
CcdbApi.cxx and testCcdbApiDownloader.cxx, so nothing needs it in the
dictionary.

Having it there makes cling parse it, which needs curl/curl.h. A runtime
environment from CVMFS has libcurl but not its headers, so loading the O2CCDB
dictionary from PyROOT fails with

  G__O2CCDB dictionary payload: fatal error: 'curl/curl.h' file not found

followed by a segmentation violation in cling's unloader. This was hit by
anchored MC in O2DPG's simulation tests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: sawenzel

CCDB/CMakeLists.txt

@@ -32,8 +32,7 @@ o2_target_root_dictionary(CCDB
                                   include/CCDB/IdPath.h
                                   include/CCDB/BasicCCDBManager.h
                                   include/CCDB/CCDBTimeStampUtils.h
-                                  include/CCDB/CCDBQuery.h
-                                  include/CCDB/CCDBDownloader.h)
+                                  include/CCDB/CCDBQuery.h)
 
 o2_add_executable(inspectccdbfile
             COMPONENT_NAME ccdb