Remove unnecessary private export macro

This was discovered during a header review of Qt 5.3.

Change-Id: Id852deb6fb5eadb43e643ac25e3b52dad7f7dd59
Reviewed-by: Liang Qi <liang.qi@digia.com>
Reviewed-by: Aaron McCarthy <mccarthy.aaron@gmail.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: I923d8eaed437dc461f98b1ed88585cc9cde528d9