Remove template leftover

Amends 33cd680ddb, which removed the
Qt5CompatiblityHook class. However, the template line above it was not
removed, and now applied to isBuiltinType. As that function should not
be a template, we remove it now.

Change-Id: If8e276daebce5480b59d9c21b049818f9a46ec98
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/kernel/qmetatype.h

@@ -1648,7 +1648,6 @@ namespace QtPrivate
         static bool registerConverter(int) { return false; }
     };
 
-    template<class T>
     Q_CORE_EXPORT bool isBuiltinType(const QByteArray &type);
 } // namespace QtPrivate