test: Remove XFAIL from tst_qwidget

  XPASS  : tst_QWidget::update() QCOMPARE(w.numPaintEvents, 1) returned TRUE unexpectedly.
     Loc: [tst_qwidget.cpp(4017)]

Change-Id: Ib7664871ed218f4c88fd2430491fa65443651927
Reviewed-by: Simo Fält <simo.falt@digia.com>
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>