Remove QT_{BEGIN,END}_HEADER macro usage

The macro was made empty in qtbase/ba3dc5f3b56d1fab6fe37fe7ae08096d7dc68bcb
and is no longer necessary or used.

Discussed-on: http://lists.qt-project.org/pipermail/development/2013-January/009284.html
Change-Id: I3202f286c119b5cb2affd0f6ef3b1ae2135b0152
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>