Cleanup unused code

Change-Id: I27821ca7e63fccd5353c48eebfde19756846dd2e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qmetatype.h

@@ -1184,7 +1184,6 @@ struct QPairVariantInterfaceConvertFunctor<std::pair<T, U> >
 }
 
 class QObject;
-class QWidget;
 
 #define QT_FORWARD_DECLARE_SHARED_POINTER_TYPES_ITER(Name) \
     template <class T> class Name; \

src/corelib/kernel/qvariant.h

@@ -513,15 +513,10 @@ protected:
 #ifndef QT_NO_DEBUG_STREAM
     friend Q_CORE_EXPORT QDebug operator<<(QDebug, const QVariant &);
 #endif
-// ### Qt6: FIXME: Remove the special Q_CC_MSVC handling, it was introduced to maintain BC for QTBUG-41810 .
-#if !defined(Q_NO_TEMPLATE_FRIENDS) && !defined(Q_CC_MSVC)
     template<typename T>
     friend inline T qvariant_cast(const QVariant &);
     template<typename T> friend struct QtPrivate::QVariantValueHelper;
 protected:
-#else
-public:
-#endif
     Private d;
     void create(int type, const void *copy);
     bool equals(const QVariant &other) const;

src/corelib/kernel/qvariant_p.h

@@ -103,11 +103,6 @@ inline T *v_cast(QVariant::Private *d, T * = nullptr)
 
 #endif
 
-enum QVariantConstructionFlags : uint {
-    Default = 0x0,
-    PointerType = 0x1
-};
-
 template <class T>
 inline void v_construct_helper(QVariant::Private *x, const T &t, std::true_type)
 {