Remove obsolete DeclareFactoryEntries

The DeclareFactoryEntries header and its macros are obsolete and no
longer needed with recent Gaudi versions.

Control/AthenaExamples/AthExHelloWorld/src/components/AthExHelloWorld_entries.cxx

 #include "../HelloAlg.h"
 #include "../HelloTool.h"
 
-#include "GaudiKernel/DeclareFactoryEntries.h"
-
 DECLARE_ALGORITHM_FACTORY( HelloAlg )
 DECLARE_TOOL_FACTORY( HelloTool )
-
-DECLARE_FACTORY_ENTRIES(AthExHelloWorld) {
-    DECLARE_ALGORITHM( HelloAlg )
-    DECLARE_TOOL( HelloTool )
-}