Remove useless content from file header

This was present since the introduction of this file in c3b185d.

Change-Id: I57bb3e7ad173f52f891dd927ac6172fce9e83c3b
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

doc/src/platforms/porting-notes.qdocinc

-pwd/****************************************************************************
+/****************************************************************************
 **
 ** Copyright (C) 2015 The Qt Company Ltd.
 ** Contact: http://www.qt.io/licensing/