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>

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -4010,10 +4010,6 @@ void tst_QWidget::update()
 
     QApplication::processEvents();
     QApplication::processEvents();
-
-#ifdef Q_OS_MAC
-    QEXPECT_FAIL(0, "Cocoa compositor says to paint this twice.", Continue);
-#endif
     QTRY_COMPARE(w.numPaintEvents, 1);
 
     QCOMPARE(w.visibleRegion(), QRegion(w.rect()));