Header cleanup in various plugins.

Change-Id: I16b273cc792bfd2035d35e7c67675f039cd387b9
Reviewed-on: http://codereview.qt.nokia.com/3185
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

src/libs/cplusplus/ModelManagerInterface.h

@@ -53,10 +53,6 @@ namespace ProjectExplorer {
     class Project;
 }
 
-namespace TextEditor {
-    class ITextEditor;
-}
-
 namespace CppTools {
     class AbstractEditorSupport;
 }