Unused include pngwrite in OpenGLContext (vcl)

Change-Id: Ib8445ed268f84d850169cc54113119308045e9df
Reviewed-on: https://gerrit.libreoffice.org/49295Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

vcl/source/opengl/OpenGLContext.cxx

@@ -15,7 +15,6 @@
 #include <vcl/syschild.hxx>
 #include <vcl/sysdata.hxx>
 
-#include <vcl/pngwrite.hxx>
 #include <vcl/bitmapaccess.hxx>
 #include <vcl/graph.hxx>