Remove unnecessary variable from feedback.pro
Remove unnecessary variable from feedback.pro

Commit 745413815893aef6060b191c09cdb143bdef2437 uses a different
deployment mechanism, so the exportheaders variable is no longer
needed.

Reviewed-by: Kalle Lehtonen
(cherry picked from commit def3f91d7c097e1c95412dedb6e1a9ebfad2224e)

qtproject/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,KDE/android-qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility