remove private qt headers

[xdch47]

Not neccesary as no #include <private/*> in the source files.

Remove qmake warning:

Project MESSAGE: This project is using private headers and will therefore be tied to this specific Qt module build version.
Project MESSAGE: Running this project against other versions of the Qt modules may crash at any arbitrary point.
Project MESSAGE: This is not a bug, but a result of using Qt internals. You have been warned!

[ddennedy]

Thanks. Private usage was removed in e494b76 but this was overlooked.