QtPrintSupport: Remove remaining LPR specific code

QtPrintSupport: Remove remaining LPR specific code

CUPS is the only supported print system on UNIX, LPR/PS support has
already been dropped but some LPR specific code still remains.

* Move qt_getCupsPrinterPaperSizes from qprinterinfo_unix to
  QCUPSSupport
* Remove qprinterinfo_unix as no longer used
* Remove LPR related code from QPdfPrintEngine
* Remove all QT_NO_LPR uses
* Remove most QT_NO_CUPS uses, use QT_NO_PRINTER where necessary

Some QT_NO_CUPS uses remain in QPdfPrintEngine, these will be removed
in a following change implementing a CUPS plugin.

Change-Id: I439b6fad9cf88c3d24aa48e49475f49ad310dbad
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>