Re-enable tst_qquickwindow::headless

With the ANGLE update in 5.7 the root cause may have been fixed.

Task-number: QTBUG-42967
Change-Id: Iec2faf5b7f5ed2c5f116a9c10ce35ed704c46d31
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

tests/auto/quick/qquickwindow/tst_qquickwindow.cpp

@@ -1348,12 +1348,6 @@ void tst_qquickwindow::headless()
         if (isGL)
             QVERIFY(!window->isSceneGraphInitialized());
     }
-#if QT_CONFIG(opengl)
-    if (QGuiApplication::platformName() == QLatin1String("windows")
-        && QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGLES) {
-        QSKIP("Crashes on Windows/ANGLE, QTBUG-42967");
-    }
-#endif
     // Destroy the native windowing system buffers
     window->destroy();
     QVERIFY(!window->handle());