QtSupport: Remove internal class QtFeatureProvider from public header.

Add header and remove export, since it is apparently not used
elsewhere.

Change-Id: I534152d7d1460a8e8f51f650d0858edf5aa5f6dd
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

src/plugins/qnx/qnxqtversion.cpp

@@ -33,6 +33,7 @@
 
 #include "qnxconstants.h"
 
+#include <coreplugin/featureprovider.h>
 #include <utils/hostosinfo.h>
 
 using namespace Qnx;