CppTools: Remove last traces of CppEditorSupport

Superseded by commit

    commit 89bd4ee3c4e4be4b39dee9ef12e798d21be3d2cb
    C++: Base parsing on editor document instead of widget

Change-Id: Iffa6e47bddc0fa3de1eab9b65fe8f711520d2d7f
Reviewed-by: Christian Stenger <christian.stenger@digia.com>