QtPrintSupport: Raise minimum supported MSVC version to 2015

Remove code for older versions and streamline #ifdefs.

Task-number: QTBUG-51673
Change-Id: Ib87b2559d0d04fcfa70cabd134ac6936a3c2a261
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

src/printsupport/kernel/qprintengine_pdf.cpp

@@ -374,7 +374,7 @@ void QPdfPrintEnginePrivate::closePrintDevice()
     if (outDevice) {
         outDevice->close();
         if (fd >= 0)
-    #if defined(Q_OS_WIN) && defined(_MSC_VER) && _MSC_VER >= 1400
+    #if defined(Q_OS_WIN) && defined(Q_CC_MSVC)
             ::_close(fd);
     #else
             ::close(fd);