C++: remove superfluous forward defines.

Change-Id: I962e0fbafdb2281645b98779a421d1084d223570
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/cpptools/cppmodelmanager.h

@@ -47,7 +47,6 @@ namespace TextEditor { class BaseTextEditorWidget; }
 namespace CppTools {
 
 class CppEditorSupport;
-class CppHighlightingSupportFactory;
 
 namespace Internal {
 

src/plugins/cpptools/cppmodelmanagerinterface.h

@@ -56,7 +56,6 @@ class ModelManagerSupport;
 class CppCompletionAssistProvider;
 class CppEditorSupport;
 class CppHighlightingSupport;
-class CppHighlightingSupportFactory;
 class CppIndexingSupport;
 
 class CPPTOOLS_EXPORT ProjectPart