Fix deprecation warning of qMetaTypeId(T *)

Since Qt-5.1, the version with an argument is deprecated:

template <typename T>
QT_DEPRECATED inline Q_DECL_CONSTEXPR int qMetaTypeId(T *)
{ return qMetaTypeId<T>(); }

see in <QtCore/qmetatype.h> line 1810 (for Qt-5.13.2).

So use qMetaTypeId<T>() without argument.