Fixes 'not win8 app' test for IE6/7

IE6/7 was barfing deleting the mock `window.Windows` object we set up
for the prior 'win8 app' test, resulting in 'Unexpected event error'
in the log, and since the `window.Windows` mock object stuck around,
'not win8 app' returned true, instead of false in IE6/7.

Tested in IE6, 7 and regression tested in FF, Safari, Chrome