CppTools: Do not put configuration document into global snapshot and working copy

These are remnants of the time when we had only one snapshot.

Change-Id: I6ff4db645d1065a0ef195834890e0774e2e2c60e
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>

src/plugins/qmakeprojectmanager/qmakeproject.cpp

@@ -461,8 +461,6 @@ void QmakeProject::updateCppCodeModel()
         }
         generators.append(proGenerators);
 
-        cppPart->files.prepend(ProjectFile(CppTools::CppModelManager::configurationFileName(),
-                                           ProjectFile::CXXSource));
         projectInfo.appendProjectPart(cppPart);
 
         if (!objcppPart->files.isEmpty()) {