Remove compiler warning when QT_NO_PRINTER is defined

This broke the build on Android with warnings-are-errors.

Change-Id: I9edb9539c4a6f7286ff46cbaa53bcfef4cf5280f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/printsupport/kernel/qplatformprintplugin.cpp

@@ -65,7 +65,9 @@ static QPlatformPrinterSupport *printerSupport = 0;
 
 static void cleanupPrinterSupport()
 {
+#ifndef QT_NO_PRINTER
     delete printerSupport;
+#endif
     printerSupport = 0;
 }