Core/Utils: Migrate further to Utils::Id

The coreplugin/id.h header is kept for downstream for now.

Change-Id: I8c44590f7b988b3770ecdc177c40783e12353e66
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/cppeditor/cppminimizableinfobars.cpp

@@ -30,15 +30,12 @@
 #include <QTimer>
 #include <QToolButton>
 
-#include <coreplugin/id.h>
-
 #include <cpptools/cpptoolssettings.h>
 
 #include <utils/infobar.h>
 #include <utils/qtcassert.h>
 #include <utils/utilsicons.h>
 
-using namespace Core;
 using namespace CppTools;
 using namespace Utils;