WindowManager: Simplify teardown
WindowManager: Simplify teardown

The direct calling of toggleGlobalEvents and toggleAriaIsolation
pre-dates this method calling clearWindows.

Calling clearWindows should clear global events and aria isolation,
if necessary. Calling those methods directly messes up the stackDepth
counter and causes toggleAriaIsolation(false) to not work properly.

Bug: T308295
Change-Id: Ie94da448582b9901e5da7a2d27ed254efcb43260

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui